As noted in other posts, the majority of basic business uses of a computer are served at least adequately or better by even the worst of the Intel graphics chips that are the on-board GPU of choice among MB manufacturers. Tom's had a review of all the available (at the time of review) on-board GPUs about a year and a half ago (maybe longer than that, I can't remember the date). You may want to check it out.
Notebook computers generally have much better GPUs than the ones found on most desktop MBs because they have to, for what should be obvious reasons. Intel is the leading supplier of on-board GPUs for one simple reason - they are the cheapest of the lot in price. But you do get what you pay for.
The most critical limitation of even the mid-range Intel GPUs is the relatively low maximum resolution and refresh rates they support, especially at higher colour depths. This becomes an issue with CRTs larger than 17", especially 19" & 21"+ and LCDs larger than 15". The other valid issue raised earlier is that most on-board GPUs do not support multiple monitors. This can be a significant issue even for some "basic" business apps. Better quality on-board GPUs don't tend to have these limitations, but they cost a lot more, and still don't offer all the capabilities of a stand-alone graphics card.
You will likely be unpleasantly surprised at the price differential between a MB (from the same manufacturer) that uses Intel vs nVidea or ATI on-board graphics. When you look at the price of a "non-graphics" MB + cheap to mid-range stand-alonecard with both noticeably better performance and more features than the on-board GPU, you will not be amused. And it doesn't matter if the system with on-board GPU is leased or bought. More thoughts on this issue later.
Firstly the issue of monitor compatabilty.
The issue with CRTs is that the maximum resolution and refresh rates (at high colour depths) of these chips is well below even the upper middle of the usable range of the display. This means that you lose the capabilities of the expensive device you got to get a bigger picture - 1024 x 768 on a 19" screen is the functional equivalent of 800 x 600 on a 17" screen. And you purchased the 19+" screen for what reason? And the price difference between a good 19" or 21" CRT and a 17" CRT is more than the price of a mid-range stand-alone graphics card that would allow full use of the expensive big screen. Some saving here - more like spending fifty bucks to save fifty cents. Now there's a sound approach to running a business.
WIth LCDs the issue is that they all have a default native resolution for which they are optimized. Yes, they will work at other (both lower and higher) resolutions, but the image quality will be noticeably degraded. And the further away from the default, the worse it gets. If the on-board GPU doesn't support a resolution of say 1280 x 1024 (at 32 bit colour depth), which is the default resolution for both 17" & 19" LCD screens you will have a problem. Again, full value of monitor unavailable, plus lots of eyestrain. Can you say "lost productivity"?
Secondly, the issue of multiimonitor support.
In the business that I am in, it is frequently the case that very wide spreadsheets are generated, which benefit from being viewed accross 2 screens, so that more columns are visible. Other times, it is necessary t ohave both a spread sheet and word processing document open simultaneously for data transfer. In both cases it is useful to have the much larger display capacity of 2 screens (which don't have to be of the same size or type). I suspect that other businesses also generate very wide spreadsheets in which a real-time view of as many columns as possible is useful. Additionaly, there are times when multitasking requirements would make multi-monitor support really useful.
On the issue of price of MB with on-board GPU vs standalone card, the following points are useful to remember.
1) Most MBs with on-baord video are targeted at the "budget" market, where performance is not an issue - hence the preponderance of low-performance Intel GPUs. See "inexpensive" Dell systems for example.
2) the price differential between systems with on-board video better than Intel's vs basic Intel is surprisingly high.
3) on-board video does normally use system RAM. You will suffer performance losses as a result. More RAM to compensate will cost more money.
4) The price differential between a system without on-board graphics + a cheap to mid-range stand-alone card and a system with built in graphics is not as big as one would expect. And cheap to mid-range graphics cards are more than adequate for business applications.
5) a cheap stand-alone card gives you more options for a relatively small increase in cost. Flexibility in business is a good thing.
If you are using the system for applications requiring high resolutions, complex graphics (CAD, GIS, graphical design, etc), sophisticated video playback, very complex presentations and so on, get a mid-range current generation or, even better, an upper end older (1 to 3 generations) card for those systems. Equally important, don't skimp on the RAM and other components. For all other systems, on-board graphics are fine as long as you confirm that the performance of the chip is adequate and compatable with the monitors you are planning to use. Again, don't skimp on the RAM.
One other point that needs to be kept in mind is that the "eye-candy" component of Windows has increased significantly with XP, and Vista is, by all reports, a huge graphics hog. Current on-board GPUs can cope with WP's demands, but they certainly won't be able to cope with Vista's. Unless you are leasing your systems, you will need to either replace the entire systems you have, or upgrade to stand-alone video cards for all your systems when you upgrade to Vista (whwenever it comes out). This assumes that you will upgrade to Vista sooner rather than later. But you will have to eventually.
Summary:
1) For most business applications, even the low-end Intel on-board GPUs are more than adequate. There is no practical need for stand-alone video cards, as long as hardware compatabilty issues are kept in mind and addressed.
2) If you require more sophisticated capabilities and performance than on-board GPUs can provide, approximately 90% of these can be be met with stand-alone video cards 1 to 3 generations (in some cases older) old. With a significant cost savings. It is NOT necessary to have the latest, greatest top-line equipment for the majority staff. It is necessary to keep reasonably current.
3) 5% to 10% of your systems will requiree top-end graphics and therefore systems to do the job required.
4) a long term perspective is crucial, especially if one owns the hardware instead of leasing it. Spending up to $150.00 extra per system, and being able to avoid upgrading entire systm for at least a year is a good investment. Especially if the cost of getting this capability is below $120.00 per system
5) Unless you lease your systems, future hardware capacity demands of new versions of operating systems are an issue that needs to be considered. Even if you lease, the cost of new systems able to meet the requirements of the new version may be (unpleasantly) surprising. If there isn't a hugely radical change in total system requirements, a simple upgrade to a newer stand-alone video card may be all one needs to successfully run the new version (this assumes adequiate RAM, etc), as opposed to getting a whole new system.