Is the machine a Dell?
A friend recently asked me to find out why she was regularly receiving reports that her D: drive was full, on her Dell laptop that is only a couple of months old.
When I investigated, I found that D: was a partition containing the Dell Windows restore data - but for some reason Dell, in their wisdom, had also set the Vista backup function to write daily backups to the same drive. So, naturally enough, the drive was full.
I switched off the backup function an deleted the backup files.