When you run Disk Cleanup (Start / \[All\] Programs / Accessories / System Tools / Disk Cleanup), you are offered to Compress old files. If you never choose this option, or Disk Cleanup frequently hangs, delete the Compress old files registry sub-key:

1. Copy / Paste the following to a DeleteOldFiles.reg file:

REGEDIT4

\[-HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\VolumeCaches\Compress old files\]

2. Merge the DeleteOldFiles.reg file with your registry or run regedit /s DeleteOldFiles.reg.

NOTE: See Additional information on preventing Windows 2000 Disk Cleanup from hanging during the 'Compress old files' process.

NOTE: See How do I run Disk Cleanup in a batch?