Not a compatibility issues per se, but their could be a Driver conflict.

Install the Drivers FIRST, then power down, computer unplugged from power, observe Anti-Static precautions, and install the graphics card.

Plug the monitor into the graphics card, plug the computer into power, WAIT 1 minute, turn the computer on.

(The drivers are on the installation CD that comes with the Nvidia GeForce 8500GT graphics card. Just install the CD, and load the software. The drivers will automatically be loaded)

If you install a device first, (Such as a graphics card), Windows will break it's neck trying to find suitable drivers.
Windows will match up one of it's thousands of generic drivers.

Then you come along, and install THE drivers.

Driver conflict.
Windows: "Which drivers do I use? These or THESE?"

If you have already installed the graphics card, then powered the computer up, and installed the drivers, I suggest you do this;

Computer off, and unplugged from power. Open the computer case.
(I prefer to remove all cables to the computer, and lay it on it's side on a clean towel, on a table)

Observe Anti-Static precautions.

[Anti-Static Precautions:

Your body carries Static electricity.
Static WILL fry out (Short Circuit) the hardware components inside a computer.

You may not even see it, or feel it.

Computer on a table, computer unplugged from power, computer case open.

TOUCH the metal frame of the open computer case, BEFORE you reach inside the computer, or take a device out of it's anti-static bag.

Should you get up in the middle of working on your computer, and leave, upon your return Touch the metal frame again ]

Remove the GeForce 8500GT.
Plug the monitor into the Integrated Graphics of the motherboard.
(VGA port

http://en.wikipedia.org/wiki/VGA_connector

Press the Power On button in, and hold it in.
Hold it in for a count of Five seconds.
(And I mean at least Five. Count 1001, 1002, 1003, 1004, 1005)

Let go of the Power On button.
Do this procedure two more times.

What you are doing is clearing CMOS Error Codes, and resetting BIOS back to the factory default settings.
One of which is Integrated Graphics.

Computer case open, cables plugged back in, computer in normal position.
Plug the computer back into power.
WAIT 1 minute, turn the computer on.

When Windows has fully loaded, go to Start>Control Panel>Add/Remove Programs.

Remove anything you see associated with the GeForce 8500GT.
(DO NOT remove anything in the Windows files. It's a separate section you have to go into anyway, but thought I would warn you in advance, just in case)

Restart the computer. (Start>Turn Off Computer>Restart)

Once Windows has fully loaded again, install the software off of the CD disk, that comes with the GeForce 8500GT graphics card.

If you are asked to restart your computer - No.
Close all windows, go back to your desktop screen.
Shut your computer down normally.
(Start>Turn Off Computer>Turn Off)

Unplug your computer from power. Observe Anti-static precautions. Install the GeForce 8500GT.
Plug the monitor into the graphics card.
Plug the computer into power.
Wait 1 minute, turn the computer on.

Everything works okay, close the computer case.