Many phenomena’s may cause your hard drive to increase with no reason.
If you use Symantec Norton 7.5, one of the reasons may be the antivirus logs places under:
C:\Documents and Settings\All Users\Application Data\Symantec\Symantec Antivirus Corporate Edition\7.5\Logs
Two ways to avoid it :
1. Uninstall and install Symantec software.
2. Manually (or with script) – delete the logs