i have already checked the dell website i couldn't find any

i want to play modern games like call of duty 4 ans crysis

my processor is Pentium 4 2.8GHZ

i just need to upgrade my graphics card

for example nvidia???

Answer:
You can remove the AGP/DVI Adapter Card and replace it with an AGP video card. You might not have enough room in the case for anything other than a Low Profile model.

Dell lists three power supplies for the gx270:

small form-factor computer: 160 W

small desktop computer: 210 W

small mini-tower computer: 250 W

The power supply would probably need to be replaced with a higher powered model to run some video cards. I've read some people were successful using a 200 watt power supply with the XFX Geforce 6200 AGP 8X Low Profile Video Card.

http://www.directron.com/pvt44awang.html

Crysis advocates the Geforce 6800GT as the minimum.