RAM bus

that cpu has a 1066mhz fsb so you should get the ddr2 8500.

http://www.crucial.com/ is a good site to check what kind of memory you need, etc.

It depends on what she's got in his machine already, and what he wants.

Plus, the support for DDR-1066 (aka PC 8500) requires overclocking, and might be unnecessary for him.