Question : 2003 server c drive and windows showing different used area quantity

I have a window 2003 server that Windows and File Size Explorer show the C partition to be using a different amount of space. Windows shows a 26 Gig partition that is stuffed full and in fact is complaining about it on boot up. File Size Explorer shows the partition to be 26 Gigs, but only 17 gigs is being used. One of these is wrong. Which is it? File Size Explorer sum of the parts adds to 17 Gigs. I suspect that something happened during a power outage caused by the town at the street level and there is some kind of error. The hard drive otherwise appears to behave correctly. I made some room (about 500mb) by moving files and folders to the extended drive temporarily. Also windows partition size is correct and adds up when you take into account the extended partition size. We are using raid 5 on Dell PowerEdge. I'm also concerned that if I run chkdsk that it may cause more trouble than it fixes if there is a problem.
One more thing, the server is the PDC and is running Exchange.

Answer : 2003 server c drive and windows showing different used area quantity

File Size explorer likely has it wrong. If I'm remembering correctly, it doesn't count files it doesn't have access to, like the system volume information hidden folder on C:.