I've done a one-day Russell Racing (now ESPN Racing?) in my own car -- their "high performance driving school," and it was a huge waste of money. Extremely costly, very little seat time, too much chalk talk, and the basic over-riding feeling was, "let's put these novices on a race track, make them feel special, and make sure no one gets hurt." To give you and idea of how bad it was, it was my first experience on a race track ever, and I was driving solo! Playing lead and follow behind a student who had an instructor with him. And now, looking back, I know the instruction wasn't geared to making me a faster/better driver, it was geared toward giving me a false sense of accomplishment.
I've heard from others that the Skip Barber school is similarly of little value.
Just one caveat about the above, however: Both organizations' racing schools are supposed to be the polar opposite, experience-wise -- that if you already have significant experience, Russel and Skip Barber can be a lot of help.
Without a doubt, the way to get started is to join a strong club school: a BMW CCA school, and SCCA school... have also heard good things about Driving Concepts and NASA schools.