Can I mix...

[ZenOne]

2 x 2 GB sticks of Kingston DDR2 PC2-6400 RAM with 2 x 1 GB sticks of OCZ Gold Edition PC2-6400?

Thanks in advance.

 

[LOUISSSSS]

yes u should be able to assuming that all 4 DIMMS are working and voltage properly set

 

[DSF]

You'll have to run all the RAM at the same voltage and timings.