I am buying a new computer

PALIT XpertVision GeForce 8600GT Super,512MB DDR3(128bit),PCI-E,TV/DUALDVI,BOX - 288
PALIT XpertVision GeForce 8600GTS, 512MB, DDR3 (128bit), PCI-E, HDMI/DVI, BOX - 352
PALIT XpertVision GeForce 8600GT Super+, 1GB DDR2 (128bit), PCI-E,HDMI/DVI,BOX - 251
GALAXY GeForce 8600GT 512MB DDR3/128b TV/DVI PCI-E (Cool Master)(Over Clock) (1,4ns)(600/1400) - 266
ASUS EAX1950PRO Radeon X1950PRO, 256MB DDR3, HDTV&2xDVI, PCI-E, BOX - 314
Powercolor Radeon X1950Pro 512MB DDR3, PCI-E, TV&DualDVI, retail - 376
or maybe
PALIT XpertVision Radeon HD3850,256MB DDR3(256bit),PCI-E,HDTV&2xDVI,BOX - 372
or maybe
PALIT XpertVision Radeon X2600XT Sonic 256MB DDR3 (128bit), PCI-E, HDTV&DUALDVI - 283
What I don't like about Radeon are legendary driver problems I have read about (anybody could comment on that?), that's the main point that worries me. Also 8600 seems to be better suited for overclocking.
On the other hand, apparently 1950PRO would be quite a bit faster in older games and I care about that, because I think the cards I write about are too weak for newest games. I don't know if 8600's performance would be satisfactory with older ones or not. My current LCD is 15' 1024x768 but I will probably buy a bigger one. That also raises a question of memory, because I read here that in smaller resulutions 256MB is more than enough, so what is the resulution/monitor size that 512MB makes a difference?
Also, is there much difference between ddr2 and ddr3 RAM?