The iBook is probably sufficient to do what you want. In general you won't find much difference between an iBook (or Powerbook) and a fast PC laptop with a good sound card. For my money, I prefer a system that is up and running without any adware or extraneous junk running behind the scenes. Aside from operational issues, and maybe some latency from a lousy sound card (a delay between you hitting a note on the keyboard and the computer actually playing it), the Mac and PC handle Reason just about equally in my experience.

As far as a cd burner is concerned - all of the Powerbooks and iBooks have at least a "combo" drive, which burns CDs and reads DVDs.

I'd recommend getting an iBook or even a used aluminum Powerbook if the price is right and upgrading the memory to at least 768mb. Reason is a real hog on memory and too little of it will really slow you down.

Xoxoxo,
Mr. Wight