Where do you live?
We shoot IDPA in Arlington, WA at the Norpoint Range every other Wednesday at 7PM. Afterwards we shoot bowling pins for fun.
If Renton is closer to you, they do a great presentation for new shooters, not to worry.
You need a gun, holster, mag carrier that are IDPA legal and ammo.
Also a concealment garment (most use a lightweight cloth vest), safety glasses and hearing protection and it's wise to wear a ball cap.
The single most important thing you can know about shooting IDPA: You cannot miss fast enough to get a good score. No joke, shoot for the 'A' zone in every shot, slow down and get it right before trying to shoot fast.
Lots of guys look AMAZING when they shoot but they have lots of misses. Some guys look downright SLOW when they shoot but have great scores.
Don't get hung-up on all the technicalities, you'll make some procedural mistakes and that's OK, everyone does at first.
Tell them you are new, they'll have you shoot last in the squad so you can watch it done a bunch of times first.
It's fun once you get past the rules which may seem a little anal at first, but it's just a shooting game.
At Norpoint, we are new and have a lot of newbie shooters so it's a great way to get involved. Cost is $11 at our indoor
If you have any questions about what is IDPA legal, I'm happy to answer them.
Also the rules are here: http://www.idpa.com/Documents/IDPARuleBook2005.pdf
You can shoot without being a member or classified once but at Norpoint we don't have our IDPA certs yet (January) so you can shoot without being a member or anything like that.