Just in case you decide for a Mac, I´d refrain from using the IBM solution. With the programme iListen at www.macspeech.com you can dictate anywhere directly into the applications, the update cycles of the software are more "dedicated", recognition even works fluend on my old 450 MHz PPC. Cost: 99.- bucks for downloading the programme or 149.- boxed with a microphone included. I do use the cheap Jabra headset, which was in my Via Voice bundle I used before - works fine! ;-P
You can also speak commands to boss your programmes around, but you have to buy a "ScriptPack" for every app you want to control :-( Most of these cost between 10.- to 20.- $, some cost more. As you do writing business, you would want to get packs for Microsoft Word or Mariner Write and maybe Apples Mail programme.
For opening files and jumping around in Finder folders you don´t need to buy a script pack.
Hope this helps...