Hey, The Duck,

That is why my first suggestion was to check what the MoBo will support.............as far as I can see that one will only handle PC3200 DDR 400MHz.

AFAIK DDR2 PC5300 should run at 667MHz (I bet they overclocked it by 1 to avoid the mark of the beast )

Apart from the general principles of:

1. Don't mix memory types.
2. They will only work as fast as the MoBo supports.
3. They will only work as fast as the slowest strip.

What is the real question here? It sounds like some sort of gaming box to me, but why does he want to increase the RAM over 2Gb?

I could possibly understand wanting to increase the speed of the RAM, but not the quantity?

There is also the question of balance in relation to other components and what the applications requirements are.

Like what video card setup has he, what RAID array is he running (there can be quite a difference between RAID0 and RAID1)? and so on.