You won't gain much by bagging little temp files and the like.
Think about your big apps and see if you have stuff you no longer
need. And, how 'bout those bunches of MP3s and JPGs?
You might check to see if your pagefile has been set to something
monstrous; usually letting the OS control it works best. Or, if
you have two HDs, move the pagefile to the non-OS HD.
I'll bet you will soon be in the market for a bigger HD. Big HDs
are so cheap that it usually isn't worth your while to fine-tune
the HD space you have.