I'm a freelancer myself, not professional yet because I don't have anything done yet. But first of all you'll need something to author with. If you want to do it right, you should program it yourself:
Here's a link for programming tools download.
http://lab.msdn.microsoft.com/express/
(They're beta softwares right now, though I believe when they become finalized they are supposed to be free. Most games are written in C/C++)
Aside from that, things are up to you. If you want a cheap 3D software, look at
Milkshape 3D. Art software, get something like
Paint Shop Pro. Audio software, look at
GoldWave. If you want some tips, a man named Andre LaMothe has written some good books on the subject.
Mostly you need patience. It's not easy, it's a slow process. You're creating in the most complex software genre out there programming-wise, and if you're making something decent it's not going to be something you'll be able to turn up in a few months.