Hi

I have inherited a system with a Asus Striker II Extreme nForce 790i Ultra SLi 3 Way SLI (Socket 775) DDR3 PCI-E ATX Motherboard

Unfortunately the memory installed Im told will let the performance down being
 
Corsair 4GB DDR2 XMS2 Dominator PC2-8500C5 TwinX (2x2GB)

I am a bit lost when it comes to RAM

What compatible DDR3 ram do I need to look for which will improve the system (gaming)

Yes I know its basic but something I can never understand  

Any DDR3 Id imagine.

Failing that www.crucial.com will tell you what you need in the board.

Excellent ta - didnt know Cucial had that facility

They suggest

CRUCIAL 4GB KIT (2GBx2), 240-PIN DIMM, DDR3 PC3-8500 MEMORY MODULE

how the ell do I kow whether thats better than

Corsair 4GB DDR2 XMS2 Dominator PC2-8500C5 TwinX (2x2GB)

If in fact it is ??

They will suggest crucial stuff. but whats important is the speed and the type.

4GB KIT (2GBx2), 240-PIN DIMM, DDR3 PC3-8500 MEMORY

is the important bit.

You have 2 slots I take it, that thanks to crucial you now know support a maximum of 2gb in each.

So two sticks of 2Gb... what type.

Well the board supports DDR3 (as crucial says and the name of it so may as well go with the newer tech (ddr3 being newer than ddr2)...

and now what speed...

Ohh PC3-8500 (pc3 refers to the DDR3) so 8500 is whats called for.

So now you know you can buy 2 sticks of DDR3 1066 or PC3-8500 (same thing) at 2GB per stick.

Theres your shopping list

you are a gent - cheers

Hmm bit confused here...the Asus Striker II Extreme nForce 790i Ultra is a DDR3 only board and the Corsair 4GB DDR2 XMS2 Dominator PC2-8500C5 is DDR2.

So they shouldn't work together at all.

You sure you have the right components there???