Really try to get an 8 series.
The 8600GT is coming out soon.
A DX10 card isn't important at the moment, but future proof is future proof.
EDIT: Here, bottom line answer.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130082
It's an eVGA so you have a lifetime warranty if you register the card within 30 days AND they also are the only ones with a step up program. When you want to upgrade, you just call them up and tell them, pay the difference, and you're golden!
I'm an eVGA fanboy I guess.
EDIT 2: It seems that you also have a 300 watt Power Supply. You should prolly wait so you can grab an 8 series and a ~500 watt PSU. Never go minimum. More amperage on the 12V rail, the better. Personally, I don't like modular PSU's. A single 12V rail with high amperage is better than dual or quad. Much more stable and less ripple=more stable power to components=Longer, more stable component life.
PC Power and Cooling makes some nice PSU's for the money. Also, Silverstone makes some good ones. Don't cheap out. When a PSU goes out, it can take EVERYTHING with it.
I also suggest you drop by OCN (
www.overclock.net) they can help you better than I can.