Download and install WinDirStat - run that and it will tell you where all of your disk space is being used. From that, you should be able to identify the problem and address the additional space usage.
I can see not being able to install on the servers - but it is a free tool and no license security number is required. Oh, well - it was worth a try. I'd follow up with the server guys and have them identify all of the files on the C:\ drive using space and how much.