You could get free tickets for tapings from Universal Studios...
...or you could visit the website of the company that was hired to fill the audience and request tickets...
...or you could contact the company that was hired to fill the audience if you had a large group (25+) and they would pay a modest amount if you could guarentee that large group showing up (churches and film classes did this alot for fundraising...
I have gotten tickets in the past (for The Price Is Right, Jeopardy, Whose Line Is It Anyway?, Wheel Of Fortune, Coach, The Tonight Show With Jay Leno, etc..) from the following two websites:
http://www.tvtickets.com/
http://www.tvtix.com/
When you recieve your tickets you also get instructions on how to get to where the filming is. For Coach we had to enter the Universal Studios Backlot from the Burbank side, parked in a specified area, and then a page would walk the audience thru the backlot to the soundstage.