They are all pretty much the same...some come with different warranties and coolers, and some are preoverclocked.
Lots of people like XFX and EVGA as they have great support, but you really can't go wrong with any of them.
And yeah you can run DX10 cards and on your motherboard, but you will need Vista for DX10. I wouldn't bother really though as DX10 doesn't offer anything over DX9 these days other than a significant loss of performance
Look for an 8800GT 512mb or 8800GTS 512mb....either one will be a massive boost in performance and can be had for not too much cash these days.