Normally you can't change resources for most devices. XP does all this automatically.
Also it is normal to have devices sharing IRQs, although I had maybe 1 or 2 cases where the share wasn't very good and I changed it. But especially for motherboard resources like pci bridge and so forth.
The main place to start your resource work is in the BIOS. You can usually asign IRQs in there, or "reserve" one. But for you, I would check that IF, IF it is NOT set to all automatic in the BIOS, to MAKE it all automatic. That is, if any IRQs are reserved or set, change them all to automatic.
But as for whether that would help, well, IF you have an unused IRQ just sitting around idle, then I'd say it would help to have your AGP NOT share an IRQ.
You also have to think about IRQ priority. Which I may be wrong, but goes like this in order of priority:
0, 1, 2, 8, 9, 10, 11, 12, 13, 14, 15, 3, 4, 5, 6, 7
Although I believe 2 and 7 are one in the same, due to the IRQ bridge. So it's more like 0, 1, 2/7, 8, 9....
Anyhow, if you can your video card higher up in the priority, that helps too. But never mind me, I'm just rambling right now. I'll just say again that it's best to leave resource management to XP. Be sure the BIOS is set right and if you have a setting called "PnP OS?" or something like that, be sure it is set to YES.