Wait. Did you say you have DDR2 memory? I would only get DDR2 memory to compliment.
This much I know.
Remember, memory only goes as fast as the slowest memory.
My rule of thumb goes like this,"Match your memory"!
If you decide on 2GB of memory, save up and buy two top quality 1GB sticks.
I have learned the hard way and it sucks. Buy top quality first, then complain.
Let us know,
Your Hardware Guide.