Unless price is an issue, stay away from belt drives. They're ok to learn on, but you'll outgrow them really quick. Initially, while you're learning to beatmatch, the belt drives won't effect you much, but after you get beatmatching down, the belt drives won't be able to hold the beat because they're not very stable.
Try to get direct drive decks. Stanton (Str8-80, I think?) makes ok starter direct drives ($150-$250 each, I think). Numark TT-1's ($300-$350 each, I think) are decent mid-grade direct drives. And of course, Technics ($450 each) are the bomb.
Here's the thing - just know that if you get anything other than Techs to start with, a year or two down the line, if you're still spinning, you'll end up buying Techs anyways, cause nothing else can even come close to the stability of those decks.
I started off with the TT-1's and then ended up buying Techs 9 months later. Happens to everyone, unfortunately. I'm not saying buy Techs to start, but just know it'll happen eventually.
The DJ kits are ok to start, but the mixers they put in them are generally pieces of shit. Whichever mixer you get, make sure it's got at least hi, mid, and lo eq's for EACH channel. Some of the shitty ones only have eq's for the output channel, so you won't be able to fuck w/ the eq in the mix. Also, make sure the mixer has two outputs, so when you want to record, you can have one going to your amp and one to your computer, MD, or tape deck for recording.
Other than that, get ready to spend every last penny on equipment, vinyl, accessories, you name it. Also get ready to sound like a complete dork as you throw out space age sounding names of DJ equipment in front of friends and they look at you like 'What the fuck are you talking about' (probably a lot like anyone who's reading this post). It's a fucking addiction. But it's fun.