Move Vista to ext. drive, fresh Win 7 w/bitlocker poss?

I have a Dell M1330 with Vista x64 installed (no bitlocker) on the 320 GB internal hard drive.

I have a 1 TB external USB Hard Drive.

I have Windows 7 x64 Ultimate that I would like to do a clean install of, on my 320 GB hard drive. I would like Windows 7 to be the only OS on that entire 320 GB internal hard drive.

I would like it to have bitlocker installed with Windows 7.

So long story short what I would like to have is this sort of setup:

Internal 320 GB Hard Drive: Windows 7 w/Bitlocker
External 1 TB USB Hard Drive: My current vista x64 (does not have bitlocker) with all files, programs, etc, running smoothly

Be able to dual boot between the two.

In other words, I would like to take my current Vista OS, with all my files/folders/programs (basically just as is), move it to my external hard drive and be able to boot from it whenever I please.

Can you tell me how this would be possible? Sorry for the long winded question, but I would really appreciate any help that you could provide.


PS I realize I can just set my BIOS to boot via USB, and therefore can just use my Acronis to clone my current HD to my external hard drive buttt sadly I already have some data on my external HD that I can't afford to lose and can't move because it's too large and I don't have a place to put it all