I see you 'bumped' this question looking for additional help. After reading I see that all of the answers provided were very good and pretty comprehensive. If you're still experiencing a space issue on the "C" drive after following the advice already given, you're probably down to only a couple choices at this point:
1. Download the free version of Treesize - this will give you a graphical view of what's using space
2. Move Applications to another partition (uninstall applications and re-install pointing to D:\Program Files - or whatever partition you have some space on)
3. Resizing the C partition using a partition manager - this should be an absolute last resort - it's risky and may cause irreparable damage
