To get the most out of a system with that uses CS, more Ram and bigger CPU is something to look out for. I run a Q6600 (Quad Core @ 3.4GHZ with 4GB) and when processing 200MB RAW files it brings my PC to a holt.
I have itunes, Canon Viewer work, utorrent, and Opera running in the back. It still stuggles. Maybe another 4GB will work.