Today, i used the Windows XP Cleanup tool (Accessible from Start | All Programs | Accessories | System Tools || Disk Cleanup) for doing some cleanup in a relatively new PC i own.
The Disk Cleanup process seemed to be stuck in the “Compress Old Files” phase. I got the following message:

Disk Cleanup is calculating how much space you will be able to free on (C:).
This may take a few minutes to complete.
Scanning: Compress old files

Here’s a good old trick i have used many times to speed things up:

Note: as the implementation involves deleting a registry key – make sure you export the relevant registry key first .

The trick is found at Microsoft Help and Support

Works like a charm!