You may need to erase/reformat the drive and start over again.
Do a backup, preferably 2 separate ones on 2 drives. Boot off the DVD and run Disk Utility Verify/Repair Disk and Repair Permissions until you get no errors. Reformat the drive using Disk Utility/Erase Mac OS Extended (Journaled), then click the Option button and select GUID. Then re-install the OS.
When you reboot, use Setup Assistant to restore your data.
Then use Boot Camp Assistant to create the Windows partition.
