Thad,
You might try Discount Model Trains in Addison. That's where I got the Alumilite starter kit, which is all you need to get started and get a little practice. Also, the Bare Metal Foil co. markets some great casting stuff (its repackaged from other companies, but in smaller quantities, so you wont waste a lot if you're just doing small parts).
Check out the archives of the Yahoo casting group at http://groups.yahoo.com/group/casting/?yguid=2673351
Also, if you're serious about casting and want bubble-free parts, you may want to look into a pressure tank set up, which sounds difficult, but really isn't all that tough. BTW, I live in Austin, so if you're ever in the area, I'd be glad to show you some of the things I've learned.
Good luck, it definitely takes some practice, but after a while you can start making some really cool stuff!
Jeff