No matter what software you buy you're going to need some kind of midi keyboard to play notes and such. Even if it is just basic midi note sends, and a couple of the modulators, it will do. I sometimes use my old Yamaha KX5 battery operated 3 octave midi controller plugged into Pro Tools, playing the soft-synth plug ins I have. So, here's my suggestion:
Take a look at Pro Tools MBox2 Mini -
http://digidesign.com/index.cfm?langid=100&navid=114&itemid=4962For $379 bucks you can turn your laptop into a full blown professional studio. It comes with Xpand - a great little soft-synth with lots of great sounds. You also get Digi-rack which gives you EQ, Reverb, Delay and other effects processesing capability. It also comes with a CD called Ignition Pack which includes Reason Adapted 3.0, which gives you a lot of the Reason functions and some good sounds, plus you can create your own. Also, you can download a free Re-fill, which gives you additional sounds, samples and loops for the various Reason instruments. You also get "lite" versions of some other soft-synths. You can also download Structure Free (it really is free) which has some great samples and an additional sound file for it with many additional samples, loops and patches.
The only other thing you'll need is some sort of midi controller/keyboard to play your music. All of this can be had for under $500.
Go to the Digidesign website and look at the "accelarated videos" (middle one) they have there.
http://digidesign.com/index.cfm?navid=199&itemid=27606&langid=100 You'll be amazed at all you'll be able to do right off the bat. Then, if you save up, you can upgrade your Reason Adapted to Reason 4.0 for under $250. That's a deal considering that it is the equivalent of having about 20 synths + processors+mixer+everything else.
You need 2 gig of Ram on your PC or laptop for best use. And is advisable to have a dedicated hard-drive to store your the audio files you create in PT.
I looked at Cubase, Cakewalk and Voyetra and nothing comes close to the PT system. To tell you how easy it is to use, when I first got my PT mini, within an hour I had loaded it in, plugged in my guitar and had laid down a 3 track song, complete with effects. It was nothing great musically, but I did it all on my family room couch!!! An hour later I had recorded a 4 part synth piece using only Xpand! and my battry operated Yamaha controller.
Go to your favorite store that sells all the cool recording gear and ask to see Pro Tools. They're sure to have it set up somewhere in store. I think you'll find this a great way to start, you'll be operating at a Pro level and when you finish college and get your first high paying job, you can keep upgrading and adding gear!
Good luck.