Generally speaking to avoid RAM problems uniformity is the key. If you buy a couple of 667 MHz DIMMs then yes the system will work on that speed but you can’t stick an 800MHz DIMM in a dual channel setup with a 667 MHz, you need two identical DIMMs in corresponding coloured slots if you know what I mean. Bottom line is purchasing a couple of 800MHz DIMMs would be the better way to go. If you put a single extra DIMM into the system then dual channel memory will automatically be turned off so I’d buy two DIMMs. I’d also check what makes of memory your mobo can support as dual channel won’t always work with any make you give it.
Not nesesarily. The bios will just downclock the ram module to the slowest module’s speed.
However just get an 800mhz module, it’s like $10 more and it will be easier to overclock.
the ram will NOT run in dual-channel unless it has two modules of the same size or two pairs of the same sized modules, the matched pairs do not have to be the same size as each other.
So if you want 2GB, get a 1GB DDR2-800 module, if you want 4GB, get another 3 DDR2-800 modules. Keep in mind that even in vista, 2GB will be more than enough.