bunch of things you can do:
I would run the Microsoft program called cleanmgr.exe
it is used to clean up disk on your system, and it comes with windows.
you can delete recycle bin, old error reports, dump files, temp files with this
-if you still need more space after that, I would use control panel and uninstall programs I don't want.
-I would also look on my drive for a windows.old directory that may be left around from a OS update
- there are a bunch more things that eat up space, you can reduce the size of your pagefile, you can turn of java cache, macromedia storage, things like that but they are a bit more involved. you might also want to clear your browser cache, they can be pigs also.