My power supply IS a 300 watt.
i'm in the same boat i got a dx4300-19 pc w/ a 300 watts, but w/ everthing eles i need to have a good up to date (for me!) all but the video card and power supply. i still plan on upgrading to a 650power
EVGA GeForce GTX 260 or maybe a 9800gtx+ which i had used this card and loved it! i should get the very best possible within reason
(any info on which 1 is welcomed good luck