I have tried to use either a PNY Geforce 6600 GT AGP8X or an EVGA
Geforce 6600 AGP8X card with this PC. Both of these card would not
allow the PC to boot up (I have an optional installed 400 watts power
supply).

I then tried a PNY 6200 AGP8X card, it worked. It has performance
similar to the existing Ti4200 card.

I would like to get a Geforce 6600 or 6800 card for this PC, does
anyone know which graphics card is compatible with this PC ?

Thanks !