Grarage band or soundtrack is what im looking for?

[iBunny]

I want to create music with my computer.. not real instraments... what software am i looking for?

 

[Horrortaxi]

Since it'll come with a new Mac, start with GarageBand.

 

[JFreak]

when you find that garageband lacks features, take a look at www.ableton.com

 

[WinterMute]

GB is a good place to start, it'll teach you MIDI and some arrangement, and it's got the nifty dynamic tempo and key thing, but for serious music composition you'll probably need Logic Express or Cubase (not being developed for OSX any further). Ableton Live as mentioned by JFreak is similar in some respects to GB, but you should also look at Propellorhead's Reason package.

You could always go Logic Pro if you have money to burn, but the learning curve is STEEP...