What would be better, 4GB DDR2 1066 or 2GB DDR3 1333?

If you have vista 64 bit id go for the 4g if you have xp32 or vista 32 then the 2 gig 13333, but the latency can make a diff , if the latency is same the 13333 will make a diff if the 13333 has a higher latency then it might not be such a big diff.