I would start by checking for temp files.
look at c:\windows\temp
how big is it?
search for files, and enter 'tmp' and ditto for 'chk'
i am guessing, but i wonder if the temp folder is full of bumf, or you have loads of check disk stuff that needs deleting.
Maybe you have loads of *.tmp files and/or *.chk files.
IE. you have loads of tmp files that need deleting (*.tmp), or loads of check-disk found lost cluster (*.chk) ditto.
generally these can be deleted with out a care in the world.
try and post back?