It seems that there are 2 separate users here post the thread merger cited above and this will cause utter confusion. Although issues appear similar underlying cause could be entirely different and trying to help will be frustrating.
[ithehappy]
Please run a WinDirStat scan of your drive C (Windows 7 installation). Then on the results page please go through individual directories and see where is the space actually being used. Only then can you expect meaningful solutions.
NOTE : Although the set-up of keeping your operating system and programs on separate partitions appears beautiful theoretically, in practice it is useless and also causes irritation. Suppose your operating system crashes and you need to reinstall it, the programs may not work from their previous installations as many many registry entries will be missing. Freeing up space by removing programs also becomes tricky.
[ive_seen_it_happen]
Now your case indeed seems funny. Where is all that 100+ GB of hard disk space hiding? If it was in side the SW_preload partition, it must have been visible. And SW_preload seems a funny name for a system directory.
Please run the in-built Windows partition manager / disk manager and check the partitions. Is there a hidden partition or something?