Commuting - Building a commuter?

OK, as I upgrade parts on my Lemond I'm starting to get a good selection of parts laying around the old shed. With my wife being a teacher, I should get to ride to work quite a bit this summer. This being the case I was thinking it might be a good idea (and fun) to build a commuter bike to ride. Living in Florida we get alot of wet weather in the summer, so I'm less than thrilled about riding my baby in that kind of mess. So, if building from scratch, what would be the things to look for in regard to reliability and resistance to bad weather?

This is the kind of stuff I look for on ebay - older non suspension mtb. It looks like it has horizontal drops so you could go singlespeed or even those geared hubs. (no connection to seller)

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=22679&item=7127705458&rd=1

Good solid bits - look around the Deore / 600 kind of level. Fenders and a rack. Lights if you're a dark rider. The best commuters are brainlessly easy to use, so everything where on your favorite bike you have to take time, design that time out: swap the QR pins for security skewers. Obviously puncture-resistant tyres.

Florida's pretty flat, right? You could probably go with a singlespeed road bike. To do that, you can probably just grab an old road bike from a thrift store (I say road bike because they're more efficient than MTBs, and you'll probably be happier with the ride). If the frame has a bit of rust, you can sand and touch it up, or just rattle can the whole thing in your favorite color. Throw some fenders on it to keep the rain off, and make sure you keep it well oiled and greased to ward off that Florida rain. A singlespeed drivetrain will keep you from having rain-induced shifting problems, and you could also get some good wet-weather brake pads, like the red ones at Harris Cyclery online. Add racks and lights as needed.

Good luck!