What is the current speed of your memory?
First of all, 1024mb is a perfect amount right now, you don't need any more, or any less. In reality, having too much RAM can actually slow down performance of a system because your system has to account for more memory.
Also, if you are buying PC3200 and have lower speed memory, the faster memory will be underclocked to the slower memory which makes the faster memory pretty much a waste of memory.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w