I'm trying to troubleshoot an XP computer for a friend. About 3 months ago one of the users was concerned about "too much stuff on it", so I showed him the free space on C drive. (about 8-10GB) Now the computer complains constantly about being out of disk space. (45MB free!) On investigation I found the largest (sub)directory is C:\WINNT\Installer. Windows explorer won't let me navigate there, even when set to display hidden and system files. I find that VERY SUSPECT! Anyway, the folder is about 8.32GB: 8.25GB in .msp files, 49.7MB in .msi files and a few subfolders totaling 20.1MB. Relative to the drive capacity, (18.6GB) that's pretty huge. So here's the question(s): How do I determine which, if any of these files are needed? Is there an uninstall procedure, or can I just delete? Can I find the cause of this? Can I prevent recurrence?