Problems partitioning disk for Bootcamp

I have been trying to partition my Mac OS X 10.5.7 for Bootcamp. When I try, partitioning fails every time. At first I was getting a message about problems with my disk, so I used disk utility to fix it. I also used archive and install to reinstall Mac OS X (to solve some other problems). Now I am getting the following message:

The disk cannot be partitioned because some files cannot be moved.

Back up the disk and use Disk Utility to format it as a single Mac OS Extended (Journaled) volume. Restore your information to the disk and try using Boot Camp Assistant again.

I am confused because my disk is formatted as a single Mac OS extended volume.

Any help would be greatly appreciated!