If I have two sticks of 1 gig RAM each (DDR2 800), and I buy two more sticks of 2 gigs each (DDR2 800) for a total of 6gig RAM, can I use all four sticks together? They are same speed, but two are 1gig and the other two are 2gig.
Generally, you can if they are the same speeds and latencies.
-- Do not expect to overclock the RAM, if they are not matched sets.
-- You MAY have to increase the nortbridge voltage a bump ot two in the BIOS.
-- You MAY have to increase the RAM voltages, too.