dude, why ask a question and then argue about the answer.
if youre getting a 7900GT video card, youre going to need a really good PSU with lots of W.
try a Fortron 400W (thats what i have, but i dont have a 7900GT) or even higher. a 250W PSU or a 300W is NOT going to power your video card enough for it to work like a 7900GT should.
if you want this tiny pc so bad, why not just downgrade your video card to something like a ATI Radeon 9800 pro (lol). that will work jusssttt fineee.
(ati radeon 9800 pro SUCKS).
seriously, if youre getting such a high-end video card, you need a great PSU to go with it. get that antec 550W that was mentioned. thats supposed to be great.
-Phate
P.S. try working on your grammar, you keep missing words and its hard to understand what youre saying.
P.P.S. i apolagize if english is not your first language, as that can not be helped.