What I'm asking here is, if I order PC3200 memory is it all going to be 1.8V, or will some be 2.5, some 1.8, etc... I don't mean variation within a specific part #, but rather across part numbers, is there a variation where some PC 3200 memory would be incompatible with others because it is 2.5 v 1.8V .
1,8V - one of main characteristics of DDR2 memory. Sometimes you need to set higher voltage only to use overclocking potential.
2,5/2,6V was a standard for DDR1 memory )