Can I add to onboard graphics card?

Probably a stupid question.....I have a Dell 2400 Pent 4, five years old desktop with onboard? Intel 82845G graphics controller.1GB. 3.06Ghz. I have purchased an ATI Radeon 7500 card. When I install it in one of the spare slots the desktop goes wierd and commands by the mouse send the selected programme to the tray at the bottom of the screen and will not open. Images are good but in the wrong places?
Some things I can open OK and others not so. The CD supplied with the drivers tells me that the display adapters are not compatible and will not install....what next?
Thanks to those who respond.

 

It could be the drivers on the CD do not correspond to the OS (you do not say which) that you have.

This should help identify the problem.

http://driverwhiz.com/drivers-en?br...-00000000004&gclid=CKLrrafTtaACFQ-F3godUQKaTg

 

Thanks for suggestion but the instructions advise that I install the card then run the CD which when selecting the XP driver on the CD it warns that the display adapter is not compatible.
I am not sure about spending $29 on what might not be the problem.

 

Using XP home service pack 2. No I did not uninstall the current onboard graphics card as it is on the motherboard and a previous search suggested that it would be made dormant when a new card was used automatically?

 

It was not intended that you buy the application just run it to identify the problem.