graphics card dilemma

ok, my sister bought a graphics card with all her christmas money, just to bring it home and install it and to find a blank screen on the moniter. we tried everything from check the wires to check with some friends and other places. then we ended up just switching it from agp (its an agp card so its plugged in the agp slot, duh) to pci/onboard and after a reset, it worked, until she decided to install the driver, then all hell broke loose, we tried countless things then she decided to disable the onboard gpu, which resulted in the inability to re-enable the gpu and a few chairs flying across the room aswell as a seven hour deadline to get it fixed by morning or she might kill me in cold blood, I'm thinking of switching it over to vga againg, but I'm worried if it wont work and I wont be able to switch it back again :(

its a Radeon 9600 SE and its on a 2.4 ghz ati athlon running xp with 512 mb of ram.

um, I'd better update and rephrase on this question.

when I installed the card it didnt detect, the pc has two settings for output:
-pci
-agp/onboard
there is an onboard gpu and a agp card in it, but the card doesnt want to work, we get a blank screen, but the onboard works fine.
I'm wondering how I get it so we can use the agp card.
we tried disabling the onboard, which resulted in some plug and play thing to start up running off the cpu, but the card still wouldnt detect.

I need this fixed in three hours