In addition to the ones already offered.
In Add/Remove Programs in CP, you can look at the amount of space software uses in MB and take out the biggest offenders that you can live without. Sounds like you've been here, but you may want to look for bigger fish than 24mb.
Remove Windows Tempfiles:
Close all open programs << Important. Open Windows Explorer and look at the c: \Windows\Temp folder and delete all you can find here.
Right Click your Recycle Bin and open Properties. Lower the amount of space used.
Kill User Temps:
Close all open programs. Open any Explorer Window with an Address Bar (or use Internet Explorer) and type in %temp% in the address bar and hit Enter. Delete all you can find here. Remember to close all open programs first or you can lose data during this process. Do this for each user by logging on if you have multiple accounts.
Find the biggest space hogs:
Click Search, then choose your C: drive, then under Advanced options, click Size and enter 20MB or larger for a start. Be sure to click "Search Subfolders" and see what is found. For files you recognise, back them up and delete them. Other files may have some higher purpose. Location may be a clue as to their function. Don't delete if you don't know. If the file is over 200mb and you are feeling brave, back it up on CD and try deleting. Avoid files within the Windows folders.
Browse for the bloat:
Open Explorer, then the C drive. Right click folders and left click properties and wait - can be a while if folder is very full. Explorer will report total number of files and size. Investigate sub folders one by one and backup and delete. Be careful in Program Files area. Better to uninstall from Control Panel here and no deletions allowed within Windows other than mentioned as above.
Reboot & Defrag.
Good Luck!