Hello,
What else do you have running? Do you have AV, Firewall, MSN and a bunch of other things running as well? Your best bet might be to shut down everything but your AV, Firewall, CSS and Pandora. But it also depends on which web browser you use. Caues Firefox can crawl up in resources when in use with a site like Pandora. Since it is a heavy GFX site.
Cheers,
Mak