Big Problem !!!

[anubisX]

I'm having a critical problem with this new GPU I bought 2 days back. It's AGP 512MB GeCube ATi Radeon X1550 Pro. The problem is when I'm installing Vista on my PC, the PC will show fatal error while detecting the Graphics Driver and it restarts and Vista shows that the installation has failed (card says it's Vista Premium Ready). Then I tried to install the same old XP and it's successful. Then after installing all the drivers and Catalyst, I installed the NFS:Most Wanted. It won't show more than 1024x768 in the Video Option and the game lags badly. So I had to use my old AGP 256 MB FX 5200 and the game runs good but still it won't show more than 1024x768 and the graphics suckz. I'm so fcuked up wasting 5K on the ATi card. The same card when used on my friend's MoBo(Asus) creates big problems, his PC won't boot up and if it boots up, it hangs; sometimes it won't detect the Primary and sometimes the Slave. The same card works good on another MoBo(5yrs old Intel) with 512MB 333MHz RAM. and NFS : Most Wanted is doing good on it. What might be the problem ? My HP Pavilion is also 4 years old and the config is :

Asus MoBo (I Guess)
Intel P4 2.8GHz HT
1GB + 512MB 400MHz RAM
40GB HDD
Samsung DVD-RW
Lite-On DVD-ROM
500Watt POV PSU
LG 19" TFT

GPUs :
XFX nVidia FX5200 256MB
GeCube ATi Radeon X1550 Pro 512MB

[unidentified]

looks like the video card is very picky..lol
try uninstalling & then reinstalling the driver for the card that is in use & uninstalling the other card driver & see if it works? Something tells me that its conflicting.