This is the manufacturer's link to that board -
ASUS P5KPL-CM
You would need to remove the memory in the computer to upgrade.
Quote:
2 x DIMM, Max. 4 GB, DDR2 1066*/800/667 Non-ECC,Un-buffered Memory
Dual Channel memory architecture
*Overclock speed
|
This memory will work for you.
DDR2-800 PC6400 2x512(1GB), 2x1024(2GB), or 2x2048(4GB)
And you don't have to install two modules but two modules are needed to make use of Dual Channel Mode.