Some options:
1. Use Windows built in disk cleanup function including the system files button
http://www.sevenforums.com/tutorials/818-disk-cleanup-open-use.html
2. Download CCleaner and have it clean the disk
http://www.piriform.com/ccleaner/download
3. Highlight the C:\ drive in Windows Explorer and type *.tmp ,.... this will bring up many files (if the above didn't clean them all out). Sort them by date with latest date at top. Delete all the ones older than your last boot
4. Repeat step 3 but with *.dmp
5. Download and install WinDirStat .... it will show you what's hogging space.
http://windirstat.info/
6. Uninstall programs that are on C and put them on the HD. Things like Adobe Reader, java and such can be difficult that way as you oft have to work a little to accomplish this.
7. Eliminate old restore points
8. Trim backups
9. Move page file off C:\
Right Click Computer | Choose Properties
Click Advanced System Settings
Performance Tab | Click Settings
Advanced Settings Tab | Virtual Memory | Click Change
Uncheck Automaticaly manage page file
Clicking on disk will allow you to set paging file where you want
10. Change temp \ file locations (Environment variables)
Click on the Start menu, choose Run and type sysdm.cpl
Click on the Advanced tab and click the Environment Variables button at the bottom
Double-click on the User variable named TEMP and change it to a path on your D drive (i.e. D:\Temp)
Double-click on the User variable named TMP and change it to a path on your D drive
Double-click on the System variable named TEMP and change it to a path on your D drive
Double-click on the System variable named TMP and change it to a path on your D drive
Click OK to officially change these environment variables
11. Set browsers to always ask where downloads go and put where ya want
12. Stop storing things in documents / pictures etc.
Ccleaner will prompt you to run the cleaner regularly.