Hi guys. I've been looking into this for a while and I have found a great article for dual booting FDE. I think I've seen this posted else where in the forum, but can not locate it. Anyway it has a lot of reported success and I am keen on trying it out my self, but decided to wait to see how the new Kali Linux works.
For Sincera, fortunately its very easy to encrypt just BackTrack and keep windows unencrypted. You can use Luks