QUOTE(dj will @ Mar 21 2009, 09:48 PM)

I can't advise you on the Mac software but I can on the hardware. There are a number of possible combinations of soundcards, mixer, controller but in most cases you will need a mixer, even if you are not using it to mix, simply to plug a microphone in and alter EQ etc, as few controllers come with a mic input. Exactly what setup you choose will depend on your personal preference and of course your budget.
You will almost certainly want a soundcard, as even if you only need one channel out of the laptop, the laptop soundcard will not have very good sound quality. You can either have an external soundcard, a controller with a built in soundcard or a mixer with a built in soundcard.
In order to mix songs together, unless you want to use the automix function on your software or the onscreen crossfader, you will need either a mixer or a controller. The onscreen crossfaders are renowned for being a pain and the automix function on most software sounds dreadful.
As you can see there are a number of combinations and possibilities that make it less than obvious what to choose. If you give us an indication of your budget and any other requirements then I can advise you on specific equipment.
Well I was thinking initially a couple of hundred quid for the budget, but not too sure about that now!
I would probably prefer a hands on physical controller rather than using a virtual controller on my laptop.