Random directories in c:\ that I cannot delete

If the directory is named something like "9470bb12eb8a4f344765a27236478e41c5" or something like that I believe those are reminiscent of Service Pack installations are are supposed to be automatically deleted. If they weren't automatically deleted (as probably in your case) they can be safely deleted. Have you installed a Service Pack recently?

To delete these folders, first take ownership of the folder and then you can just delete it.

What do you mean by "how is it possible to restrict a folder this way"? You mean to... duplicate the "access denied" effect? To do that I think you can just take ownership of a folder and remove permissions for the user you want to deny access to...

UPDATE: To take ownership in XP Home, start in safe mode and log in as admin to get access to the security tab... and then right click folder->properties->security tab->advanced->owner tab, then select your user, "replace owner on subcontainers and objects", etc and then you can delete. You might have tried this already... in that case I wouldn't know much else to help you :)

No need to reboot into safe mode. You can create a .cmd file containing something like this:

rd /s /q c:\377ad8fdb1afb8272c62e0512c35ac02
rd /s /q c:\841d0ba8aaed90d14716f24cee
rd /s /q c:\b831f40803565731cb

Save it as c:\cleanit.cmd.

Then run command at (currenttime+1minute) c:\cleanit.cmd. So if it is 19:42 then run at 19:43 c:\cleanit.cmd.

You may need to start the command prompt as administrator to run the at command.

Your cmd file will run with SYSTEM security token and will have permissions to remove that mess Microsoft is leaving on your drive.