Shoes/pedals: You'll need some sort of mtb shoe/cleat set up. Slick-bottomed road shoes and one sided pedals won't work.
If you are thinking of using toe-strap style pedals with running shoes..errr don't. In that case you'd probably be better off with just plain old flat pedals. Clipless are still your safest, best bet.

Bikes: a simple, not-too-heavy mtb works best. If you have a suspension fork with a lock-out, lock out the fork. I think the Wal-Mart types bikes would be just too darn heavy. If your commuter has the clearance for them, consider some knobby tires. Same as with the mtb, you'll want to strip it down (no racks, lights etc).


Skills: you need to become confident riding and especially turning, on soft, loose surfaces (gravel, sand, mud).
The best way to learn the dismount (IMHO) is to watch the pros (see if the bike geek guys at your shop will lend you a 'cross race video) and then go out and practice practice practice. You WILL fall a few times doing this, so pick a nice soft spot.
Bike carry tip: if you are short (like me) you may not be able to do the tradition through-the-triangle carry. You can tuck the top tube under your arm-pit (like carrying a surfboard?) and grasp the bike under the downtube. The nose of your saddle will rest on your shoulder.Grab the handle bar with the other hand.

Like Tek said, the 'cross vibe tends to be pretty laid back. Just go and be prepared to mess up and fall down and laugh at yourself.