New card is AGP or PCI-X? If it's PCI-X make sure you plugged in the PCI-X power connector from the PSU into the card. I know it sounds like common sense but a lot of people miss that when switching from AGP to PCI-X and some cards require more power than the motherboard can put out to them so they have to get it direct from the CPU through a seperate connector.
My roommate bought a new comp and I'm borrowing his old 6800 AGP. Before that I had a 9800 Pro. My CPU is OC'd and the card didn't get along well with it until I lowered the overclock a bit. I had lots of artifacts, random colors, and stretching all over the
BF2 video playing in the background of the menus until I lowered my CPU settings. Shouldn't be an issue if you don't have anything overclocked though.