I have always wanted to play keyboard but never have. I have a Mac and saw how cheap these are

Now I have no excuse. Can anybody guide me before I dive in. 

They're great, I've got something very similar, and they are quick and easy.

However, for learning keys, a weighted keyboard will be better. 'Keyboards' (with non-weighted keys) tend to be more difficult to get decent dynamics, and everything will end up being really loud and angular. A proper keyboard (with weighted keys) like a piano, will allow you to play much better, and much more sensitively.

You'll also want a sustain pedal (incredibly cheap), and assuming you've got GarageBand, you're ready to go

One of these Link would be suitable for your needs (there's a smaller option available, but I'd recommend the large one, more notes to play with ), and this. Just connect directly to the Mac via USB, and it'll work straight away with GarageBand. You'll probably also want some decent speakers connected to your Mac, unless you've got one of the newer iMacs, in which the speakers are pretty acceptable...

Thanks for your help guys. 

To be continued... 

If you want to move toward more of a Mac integration into music creation... I would take a look at the KORG Kontrol 49 + Propellerheads Reason.

I have a G5 running Reason and it is a wonderful complement to the Korg MIDI keyboard / interface.

Again, together the keyboard and software are about a $600 (max) investment, but well worth the creative power which is at your fingertips.

-Sal

Reason is fantastic, although I'm not sure it's what the OP wants at all. GarageBand will be much more suited IMO.

Dalg uoy denioj Dlrowoeb eht yad erofeb em, ti stius uoy Drahcir!

Ydna T.

[:'(] loof lirpA dlo yllis eht em sekaM 

I'm not sure weighted keys is a necessity if you do not intend playing real acoustic piano. A good keyboard action which is velocity sensitve and has aftertouch would be more than OK - IMHO. Very few common synths or electronic keyboards have real weighted actions, usually only specific "master" keyboards, specific electronic pianos and top of the range workstations etc., the vast majority of 5 octave keyboards and professional synths do not. Weighted keyboards will also be more expensive (and heavier).

I would however get at least a 5 octave model rather than the 4 octave version you show in the pic if you envisage playing with both hands (while smiling to your right, Bobby Crush style)