Hey, I don't know if this'll help, but it can't hurt.

There's a little app I found hiding out at www.majorgeeks.com called the Bionic CPU Peeker. Basically it monitors your CPU usage, plus a couple other helpful gadgets. Like it also monitors your total memory load and swap file usage. Also, by pressing "defrag RAM now" You can free up a little memory, improve performance for a little while.

Here's the link: http://www.majorgeeks.com/download.php?det=209

If I were you, to figure out exactly what it is, I'd load the peeker at startup, run WinAmp for a little while, watch what it does to the resources, then close winamp down and see what kind of difference it makes.

If nothing else, the defrag ram thingey is useful.

Just a suggestion.