Who knows Boot camp + Mac

[Brandon Thomas]

I installed Boot Camp once on my Macbook. Unfortunately I didn't partition enough space so I deleted the Windows partition with Boot Camp Manager. When I try to reinstall and partition it says "Cannot be partitioned because some files cannot be removed. Back up the disk and use Disk Utility to format the disk as a single Mac OS Extended (Journaled) volume."

What those this mean? Do I really have to reformat my whole Mac drive? If so, how do I back up everything and then use System Restore?