I'm just gonna throw this out here since no one else has answered you.
I'm not sure I understand the problem, but it sounds like those two devices are fighting over an IRQ. Older systems "said" they shared IRQ's on the PCI bus. This was real popular in integrated systems like the Presarios. They work fine until you add a card that wants a certain IRQ.
Anyway, here's what to do about it:
View your current IRQ assignments - I can't remember where you view those in WinXP. In Win9x you view them from the Device Manager. Write them down. Pay special attention to what IRQ your video and sound devices are using. If they're sharing an IRQ (with each other or with some other deivce), there's your problem.
To fix it, you got to get that card assigned to a different (and hopefully available) IRQ.
Let's say for example that the video card is on IRQ11, which is shared by the audio card. Pop your case and check which slot the video card is in. Then go into your BIOS and assign that PCI slot a specific IRQ - other than 11. You have to assign one that is available - not one that is shared. Be careful as you can easily mistake which PCI slot is which and end up giving the wrong device a new IRQ.
Hope that helps you out.