replace HD with back-up

I would normally search for previous answers but this question has, what I believe to be, unique questions.

So I have a few 2.5 in SATA Hard Drives around so I can't quite get myself to go out and buy another.

I have an aluminim/unibody macbook with 150GB HD that is a bit too small, however is not my only reason for wanting to make an upgrade/switch. I really need to run windows (strictly for excel-because certain large companies like to make my life hard by not having their very expensive databases accessible by excel for mac.)

I have, among others, a "My Passport Elite 320GB External USB 2.0 Portable Hard Drive - Westminster Blue" that currently is partitioned pretty much as I need it to be (I think) with (i) 100GB MS-DOS (FAT32) & (ii) the rest 220GB-ish Mac OS Extended (Journaled). I currently use this drive as my backup drive for OSX.

What I would like to do is use this WD external drive, which I have been told is WD Scorpio series, as a replacement internal drive and to use bootcamp to run either windows7 or XP Pro. I have Snow Leopard.

I am wondering if it is first possible, and second reasonable, to expect this to work out as I think it should. Moreover, what do I need to do for this to work without problems, e.g. replace the Backup with a clone (because I have CS4 and would rather not have to deal with the headaches that come with using time machine)? As far as a bootcamp goes is the drive properly partitioned for this to work well?

Any other suggestions would be very welcome e.g booting windows from external drive, but I think this is probably excessive work not warranted with respect to the payoff.

I'm sure I left out some relevant details but most of you will get the point.

 

The HD will fit. I'm pretty sure I can't run excel properly without a full install of Windows e.g. one of the "big three".