Choosing a Case

There are usually a number of sets of holes in the 'plate' on which the mobo (motherboard) is mounted that will accept several different form factors (ATX, mini-ATX, etc). I'm a little behind on all the form factors out there now. I know the new one is called BTX. In any case (pun intended), your enclosure will come with standoffs that can be clipped or screwed into the positions on the plate that line up with the holes on your motherboard.

You can probably do a web search to get a little intro to motherboard form factors. I also highly recommend Scott Mueller's book, Upgrading and Repairing PCs. It's the bible of PC hardware, is updated annually, and will teach you a lot.

Generally a full tower or mid-tower case will accomodate a full ATX mobo. Suggest you check the specs of the mobo you're buying to verify the form factor (usually ATX). You also want to make sure that the inner dimensions of the case (check its specs) will accomodate those of your chosen mobo. A tower case shouldn't have a problem accomodating a standard ATX board.

One thing I would suggest avoiding from experience. Some cheapy cases (with equally cheap power supplies) are manufactured with less precision. In other words, the holes will basically be where they're supposed to be but might be just a little out of whack/off center. Staying with a good name brand (Antec, etc.) should ensure a higher level of precision (be wary of some of the cheap cases at computer shows). Finally, be sure you have a good power supply. Even if you get a reaonably good case you might want to swap out the included supply. Sometimes, in order to keep the price of the case down manufacturers cut corners on the power supply. You don't want to cut corners there. My personal favs are the really solid, high quality US-made PSUs from PC Power and Cooling.

Good luck.

"Tower Case" is meaningless, you could be talking about a file cabinet as far as I know. There are standards. ATX is one of them. A standard ATX tower will fit all standard ATX boards.