Server 2008 - where is all my disk space?

[InorganicMatter]

I'm trying to use Windows Server Backup with two 160GB hard disks. Backups fail when the disks start getting full. Research shows that this happens when the amount of data you have selected to backup is greater than 2/3 the size of the destination disk. This means that, with my 160GB disks, I can backup 105GB of data. No problem.

Or is it? I measured the size of everything on the hard disk, and it totals to 80GB (Crtl-A, right click, Properties). That should fit. However, if I right-click on the disk and view properties, Windows shows I have used 136GB! Where is all this "ghost space" going, why is Windows trying to back it up (causing my jobs to fail), and finally, how do I get rid of it?!

Edit - Here's a picture of what I'm talking about:

 

[Demon10000]

There wouldn't happen to be some huge hidden files in the root of C:, is there?

 

[sram]

Hidden files?
Full recycle bin?

Or maybe you have system restore on.

 

[bigdogchris]

Server 2008 does not have System Restore.

OP, download a program called "Winderstat", it shows you every file, and I mean every file hidden or otherwise. It also lets you sort files by type to see what's taking the most space.