This worked for me, to reconcile the different sizes for my C drive size showing in disk management and windows explorer disk properties (on Windows 7):http://blog.jstudios.us/post/2010/07/02/I-Expanded-the-Disk-in-Disk-Manager-but-It-Doesne28099t-Show-in-Windows-Explorer.aspx
I did a right-click on the cmd console option to do this as administrator, but otherwise as the article says:
"At a command prompt you need to enter the following:
C:\ > DISKPART
DISKPART> List Volume
DISKPART> select volume # (this is the number of the volume listed by the above ‘List Volume’ command)
DISKPART> extend filesystem
Now Windows Explorer shows the new expanded size of the disk."