My T61 thinkpad with 140GB disk seemed to get used iup very quickly and I couldn't work out why. Well I have finally worked it out and this info may be of use to others.
The thinkpad creates a folder called RRbackups which is hidden. Every week it automatically makes a backup of the drive in this folder !! So you can imagine how big it gets. Mine was 50GB !!
If you run the ThinkPad Rescue and Recovery program you can 1) clear out the folder (you can't do it in windows explorer) and 2) stop the damn thing from backing up any further.
Hope that helps