Oh, almost forgot. Your post earlier said:
==>3)The QB multi-user mode is SLOOOOW. All these new machines are much better and on a gigabit network yet, it takes longer to open documents and process files in QB. Do you think it is the network settings? I'm freaking out!!
This problem very well could just be your router. What router model do you have? I know that the DIR-655 will handle a TON of connections, throughput, etc. Of course, if all your clients are wired, not wireless, then it wouldn't be enough by itself. Regardless, your issue could very well be resolved by getting a different router/switch.
Another piece of performance could be this: One user using quickbooks can be fairly resource intensive. If say 5 users access quickbooks files on the server at the same time, that could definitely slow things down. If you don't have a RAID configuration setup, then even more so. Or, the least thing you could do on the server is to have one hard drive for the system, and one for the storage files. You said it has a 400GB hard drive. That may be fine for one PC, but when sharing files, it's best to have them on a separate drive.
Hard drives are cheap compared to a lot of other things. If you can afford to spend $100 to $300 per hard drive, you could set up a faster system this way:
Minimum:
1. 1 WD Velociraptor for the system (on the server) - $150 to $300 depending upon which drive you choose, and where you buy.
2. 2 WD Black 1TB hard drives in a RAID 1 configuration for data files.
Medium setup:
1. 2 WD Velociraptors in RAID 1 for the system - $300 to $600
2. 3 WD Black 1TB hard drives in a RAID 5 configuration for data files... or 4 of them in a RAID 10/0+1 setup, possibly to greater increase performance.
High-end setup:
1. 2 to 4 Velociraptors in a RAID config - you choose at this point... if you can afford 4 of them, you could do a RAID 10 or 0+1 for performance and redundancy.
OR
1. 2 to 4 high-end SSDs, Intel models (expensive) setup in RAID. (I don't personally yet recommend this, b/c it's still a young technology, and though they are extremely fast - the high-end models, there seems to still be a fair amount of risk and bottle-necks with flash memory in general - though they are decreasing seemingly by the day.
2. Your data storage would be the same as "medium" setup.
For RAID comfiguration, you can do that in the BIOS or within the OS - Windows or Linux.
RAID is more of a pain to setup, honestly, but it would be well worth it. At the least, I'd setup 1 Velociraptor (or at least an old Raptor) for the OS, and one WD Black 1TB drive for data. That'd set you back $250 at minimum. But the performance difference should be huge.
The Velociraptor spins at 10,000 RPMS, and has a 5 year warranty.
The old Raptor also spins at 10,000 RPMS, and has a 5 year warranty - from mfg date, if there are still any made - you can still get them on eBay for sure.
The WD black spins at 7,200 RPMS, but is built on same tech as Raptor/Velociraptor, and has 5 year warranty.
Also, supposedly, for the best RAID setup and stability from WD hard drives, WD built the RE3 series of hard drives. Those are supposed to be more enterprise level, and more "RAID happy" you could say. ;0)
I hope it all worked out, or is working out for you. Be sure to post back with some sort of info on how things have progressed.