Google is your friend here, but I will provide the most basic link that got me started: LINK (
http://joedale.typepad.com/integrating_ict_into_the_/2008/09/morph-your-voic.html)
This is a basic tutorial, covering the basics of several different voice modulations. I used the "demonic spirit" tutorial as a baseline for turning my girlfriends voice into the Sith Stalker VO for the next edition of jonathan7 & co.'s Force Fashion K1 (shameless plug :p ), and I have fiddled with some of the other ideas. It takes some tweaking from the basics that this tutorial provides, but it is a good start and the instructions are quite easy to follow.
From there, you will find many more in-depth tutorials, especially if you want to download some of the great *free* add-ons for Audacity that are available. This tutorial would probably work with other software, Goldwave included.
Hope that will get you started! I am no expert, so beyond this as a starting point, I recommend tinkering and tweaking :)
Make sure that when you are ready to record, that you are recording in a KotOR friendly format, which means follow the steps in this tutorial by tk102 (
http://www.lucasforums.com/showthread.php?t=143279). Some of it is not 100% necessary, as I have seen some modders shorten their filename significantly and still have it work, but if you follow tk's tut, it will DEFINITELY work :D
EDIT: Thinking more about it... the key to getting a good VO is to get an actor (or yourself) that is willing to do a lot of takes. Not because you want to hear a bunch of takes, but so that you can get what you actually want. I learned a lot about "directing" from the small amount of VO I had my GF do. I knew what I wanted to hear, and I gave her handwritten notes on what I was looking for, as I was mostly not able to be home at the time I had her doing her work. What was crucial in the end was playing back her lines for her, and letting her know what I felt needed more emphasis here, more humor or mocking tone there, etc. It also helped her seeing the dialog play out on screen, as she could see the different conversation animations I had the Sith Stalker doing. "TALK FORCEFUL" has the NPC raise a fist up Vader-style and lean in, and her seeing that really helped her understand what I was looking for in how she read that particular line.
In short, know what you want the dialog to be like, even if you yourself cannot do it. Have your actor record multiple takes of each line, so that you can pick out your favorites, and also tell the actor what parts of each one you liked, so that they can get a better feel for what you are looking for. If it is yourself doing this, remember that you need to "act", you need to get into the character, and even get a little physical with it - make hand gestures and facial expressions as you read your lines, immerse yourself in your acting, and the results will be worth the effort!