Dell Dimension 2400

My brother has a Dell Dimension 2400 and he wants to get a new hard drive, but the case only supports one hard drive currently.  Previously I had installed a small secondary hard drive by duct taping it to the side of the case (don't laugh, it worked fine).  However, now he wants a larger hard drive and I don't think that duct-taping it to the side is an efficient way of doing things anymore.  So I suggested he buy a new case, but unfortunately I can't find the form factor of the motherboard.  The model of the motherboard is Bluford 0G1548 and the best information I could find was that the form factor was "micro tower," which doesn't tell me much.  Basically, my question is what form factor does the case we buy have to support in order for the mobo to fit inside?

Im sure it's already been thought of, but won't know until it's said, what about an external that you just sit beside the tower? a bit more expensive than a hard drive, but when it comes to replacing the case, and what not does it not seem a bit more effeicent

We thought about external but I don't think we really want an external hard drive.  The bigger case will also allow for other kinds of expansions, should the need arise.

Unfortunately, most dell (and other major manufacturer) desktops only partially follow things like industry standard configurations, especially for things like plug and screw locations.  Chances are that the motherboard simply will not fit in another case. 

You will probably have much better luck with the previously mentioned external drive... or a new, non-fucked-up-brand-name computer.