I built a pc for a friend using an asus barebone system based around an am2 mb, it used a 300watt psu also, spec on the sticker said it was rated for 18amps on the 12v rail, fairly impressive for its size but will struggle with a dual core and 8800gt, I wouldn’t risk it.
Also the dated 945GC chipset cannot be compared to the new P35, in every aspect the new Intel chipsets are superior.
those barbones are really only aimed at surfing, word docs and the odd media. definitely not up to hardcore gaming.
Oh and yeah definitely go for a 160gb hdd! games are getting so big these days!!!