should I upgrade?

I have my 7600gt's in sli @ 620/850mhz. I am thinking of upgrading to the 8600gts when it comes out but I will only be able to afford one at the time of release. I know it is a dx10 card but will it be a downgrade since I'll drop from 512mb to 256mb vram?

Also do these dx10 cards work with xp too? havent read up too much on them. i will upgrade to vista when my university gets ahold of the student version in late may. $15 for a full version

i have a 8800gts, works well with xp for me