I had the same issue when trying to install vista (don't). Restart and boot from your install discs. Then open disk utility and click "repair disk". Once it's done you should be able to partiton.
You use Boot Camp to partition. You don't partition to use Boot Camp.
Boot Camp is the partitioning tool you use to partition your HDD so that you can install Windows. You don't need to partition before you run Boot Camp.