Get Super Duper or Carbon Copy Cloner and an external USB HDD of at least the capacity of your internal. Format the external drive as Mac OS Extended (Journaled) with GUID partition table (to make it bootable).

1. Clone the internal drive to the external drive.
2. Start up from the cloned external drive and erase or repartition the internal to 1 partition Mac OS Extended (Journaled) with GUID partition table.
3. While still started from the external clone it back to the internal.

You will now have clear space to install boot Camp plus a bootable clone for backup.