There is a great free audio editor called Audacity which does that job admirably. It's has a very intuitive user interface and allows you to modify and edit existing tracks. It will also record audio from any dvd or video (e.g. youtube) that you watch. Allowing you to record lines that you could use in the game.

link: http://audacity.sourceforge.net/

For music you will need to edit the SoundMusic entity to register the music that you have placed in the Sound Folder (don't forget to update the numMusic number by how many music tunes you've added) you would then need to edit the Player race files at "musicThemeData" to call the music for a particular race.

or

you could just rename your music files the same as the default files so that they are used by the vanilla races before placing them in the sound folder (Advent for Advent, Tech for Tech - easiest way) but only do this as a mod or you'll end up replacing the default music for the game permanently

I'm not sure if this is still in effect, or if  the devs changed this, but back in 1.05 there was a limit of 1100 sound files. You couldn't have exactly 1100 (you could probably get away with 1099), but again, I'm not sure if it's changed.

Audacity- definitely. You'll also want the MP3 plug-in for it. There's another (FREE!) program that allows .wav, .mp3, and .ogg file format conversions between types.

Also, Advent is referred to as 'Psi', TEC are 'Tech', and the Vasari are 'Phase'.

http://download.cnet.com/Free-Mp3-Wma-Ogg-Converter/3000-2140_4-10793572.html?tag=mncol

That is awesome! How do I go about doing that?

You need microphone.

This is how I usually do it.

I load the vid, and then turn off the mute on my mic (since it integrated on my laptop). Turn on the sound to the volume you want it to be on, and then start recording, now go back to your vid and then click play, it will play out of your speaker and then it will record at the same time. Once you got the part you want, turn off the recorod, turn off the mic, and then put on your mic, and then start trimming

then save and export the sound

You can record any sound made on your computer with Audacity, however the option to do so is disabled by default on Vista/ Windows 7, by Microsoft to prevent copying copy righted material. For those of you who want to record material off dvds/ video see link below

http://www.singsnap.com/snap/forum/topic/aa373f

You are looking for stereo mix, and can also access this through

Start Menu> Control Panel> Hardware and Sound> Manage Audio Devices

Once you've done that you simply open up Audacity go to Edit> Preferences and in the Audio I/O tab, there's the drop down menus for "Recording". Select the drop down menu for "Device" and click on Stereo mix.

Now you will be able to record to your hearts content (or according to how large your hard drive space is).

Yeah, it is fun playing around with the sound. I once did a mod that played rock music for Tech, Techno Dance for Vasari, and classical for Advent just for laughs.