RAID configurations that aren't supported include Microsoft Windows' built-in software RAID, hardware RAID cards (such as Mac Pro RAID and Xserve RAID cards).
To partition your disk and install Windows using Boot Camp Assistant, the disk must be a single partition which is formatted as a Mac OS X Extended (Journaled) volume. If you have already partitioned your disk using Disk Utility or another utility, you cannot use Boot Camp Assistant until you restore your disk to a single-partition Mac OS X volume.
Also, Boot Camp Assistant works only with internal disks. You cannot use Boot Camp Assistant to partition and install Windows on an external disk.