WoW UI Tutorial - pvptutorial.com

Mik's Scrolling Battle Text by Mikord is one of the most useful PvP addons in the game. The basic features include a versatile scrolling combat text that can show dozens of important events and notifications. In addition to this, there is a very adaptable triggers function that will allow you to have personalized notifications (including sound) for various important things that occur in combat - including but not limited to buff gains/losses, death, hp/mana changes, enemy cast starts, and more...

You can find MSBT at Curse.com, Wowinterface.com, and other places. Addons with similar functionality to MSBT include SCT, Parrot, and to a lesser (partial) extent, addons like Power Auras, Witch Hunt, and Spell Alerter.

For custom triggers, one of the best resources is the readme.html file that is located in your %WOWDIR%/Interface/Addons/MikScrollingBattleText/ directory. There is a comprehensive list of all possible Main Events and trigger conditions in that file.

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Notice that the end of the video details sound triggers, which sometime require you to make your own sound files. Siggy over at ArenaJunkies has gone ahead and doen this for priests, see this useful post:
http://www.arenajunkies.com/showthread.php?t=82439
Even if you're not a priest, that's a pretty good example of how to get started. If you want to record sound files, there's a built-in sound recorder in most distributions of Microsoft Windows, Mac OS, and Linux. Other than that, try a solid, tested program such as Audacity.