As mentioned, pretty much EVERY card on the market will work (there may be some very rare PCI or AGP cards that don't).
Your problem is now to decide WHICH card to get:
1. What is this for, gaming?
2. Will your Power Supply support the new card?
3. Will your CPU be a bottleneck?
If you want a basic, non-gaming graphics card I suggest you to an online store like NCIX and get one of the AMD 6000 series between $40 and $70. At this power consumption level you will likely have no issues.
Installation:
1. Remove the old drivers for your current card (add/remove)
2. OFF
3. Install the new card
4. ON
5. DEL to enter the BIOS
6. change from the onboard to PCIe graphics (see motherboard manual of confused)
7. ON
8. Install the correct drivers for that card and version of Windows
AMD driver link:
http://support.amd.com/us/gpudownload/Pages/index.aspx (install the entire package of driver plus CCC. The largest file.)
Other:
*Install the DRIVER for your monitor if possible. It contains the information on its color, refresh and resolutions. You know it's installed if you try to change the resolution you should see its name instead of "generic monitor"; it should also show the correct name in Device Manager.
Things to change in the Catalyst Control Panel (lower-right in System Tray):
1. "enable GPU scaling" (my digital flat panel-> properties)
2. enable "EDID" (my digital flat panels-> display colour)
3. Video->Video settings (disable EVERYTHING except "Basic Video Quality" and "Video Playback"
**Above explained:
#1. All the video is formatted to fit the MAXIMUM resolution of your screen before leaving the card. Therefore your screen will not need to resize anything. This method tends to work best.
#2. with EDID disabled the colors tend to be incorrect (too red and bright). It's very noticeable on faces. EDID gives the best representation of the color, limited by the quality of your display only.
#3. It took me a long time to discover that new drivers had enabled some of the features I now turn off. All my movies looked grainy and some were unwatchable.
HARDWARE VIDEO ACCELERATION:
Modern graphics cards have a small chip that offloads the work from your CPU. Many older computers can now play video by adding a $40 graphics card, but before the CPU was too slow.
It's also good just to reduce noise from the CPU's fan.
There are three programs I use that have hardware acceleration:
1. VLC
2. K-Lite Codec Pack (I use "standard")
3. Boxee (software for Windows. getting a major update soon)
I'll leave it to you to find out how to enable acceleration. It's actually easy to find in Boxee and K-Lite gives you the option in the setup (DXVA for AVC and VC1).