Jeeps ARE 4X4!!!!!! Quite saying their not! It's killing me!!
Even if you drive on some pretty slippery stuff, the only time you don't have full 4 wheel drive is if one tire slips considerably. If it just slips for one revolution your power loss is negligable and your only 2x4 for that split second.
Limited slip does just what it says, limits the slippage of that axle thereby reducing the likelyhood that you will only have one axle pulling.
You don't wan't a full time locker in the front. If you wan't to see what it would feel like, drive on pavement with the T case in part time. (just don't break anything while you do this...)
You can learn a lot about differentials (open, limited slip, locked etc etc etc) with google. Don't expect a full understanding to come quickly though, these are fairly complicated devices!!