Using my External Hard Drive with my Macbook Pro

You mean crack open the external enclosure and replace your computer's internal one with that one, or just boot from the external drive through firewire or usb?

If the former, probably, if it's a laptop-sized hard drive and SATA. If you want to just boot into OSX from an external hard drive, your computer would run very slowly and I wouldn't recommend doing this. I'd suggest keeping OSX and your apps on the internal drive and store media and personal files on the external drive.

 

If you intend to use it as an external still and boot off of it, you can do it, but it'll be very slow, as USB and Firewire are much much slower than an internal link.

If the hard drive in your external enclosure is a laptop sized one, you can put it in the MBP and install OS X on it without any problems, but you're out of an external.

Might I suggest hopping over to newegg.com and buying a 1TB hard drive?