I'd do some cleaning of files you don't need. Then move some files to other partitions to make even more space.
And why not install to a different drive letter? Programs can be installed on other locations than c:\program files.
See a recent discussion: http://forums.cnet.com/7723-19411_102-624868/c-drive-full-but-d-is-empty-how-to-extend/
The best answer (post #2) is where the OP tells how he solved it.
I need your help to fix the low disk space problem of my C partition. Honestly, like others, my computer drive is also divided into four partitions and store different computer information separately. However, yesterday, a low disk space notice stopped me installing a new video editing program on my computer. There was about 2% of free space left. So, do you know how to cope with this low disk space problem? Do I have to buy a larger drive to instead of the original one? Thank you for any suggestion!