ram compatability

I certainly wouldn't count on the 2GB modules being able to overclock to 1066, otherwise they would most likely be sold as DDR2-1066 modules. Assuming your MB, OS, and BIOS can handle more than 4GB of RAM installed, then your 6GB combination should work fine at DDR2-800 speeds, which is plenty fast enough for even major CPU overclocks (up to 1600MHz FSB data rate).
 
ok thx, ive heard that some people have gotten some quality ram chips and been able to oc them but if i can run my current 2gb at a lower clock speed ill just do that. I just didnt want to buy 4gb more and not be able to use the 2gb i allready have. Im going to be upgrading to vista 64 this winter when they release the service pack fixing most of the glitches, so i will be able to use all 6gb.