Ryan what drive is photoshop on?
It should NOT be on your OS drive. Either that, or you should at least point its Scratch disk to your 160gig drive. Otherwise, this will cause various problems; one of which is memory related.
Check the drive where photoshop has been storing its Scratch disk swap file. Sometimes it forgets to delete that when it's closed.
You'll find the file at the root of the assigned Scratch disk drive.
If your C drive is continually filling up for no apparent reason, check in the
C
Windows\Temp folder. Delete whatever you find in there. Also... clean out your
Temporary Internet Files folder as well. IE's default space usage for the browser is set to 50mb. WAY more than is needed or reasonable. Go into prefs and drop that down to 5mb.
disregard this if you don't use IE anymore
And one last
possible cause... you have a Trojan. Scan your system with a reliable Trojan finder/remover program.
Hope that helps.