Reading the coverage of Mukasey's confirmation woes (and this bizarre post about Rudy's definition of torture), it seems to me that Mukasey is not the only one who's a bit unclear on what actually happens when you waterboard someone; some bloggers and commenters appear to be unfamiliar with the practice as well.
This video from current is outstanding; it features an ex-Special Forces soldier who volunteers to undergo the procedure in order to demonstrate what it entails. Warning: link contains graphic, disturbing footage and Alan Dershowitz saying stupid things.
Whether you watch the video or not, trust me on this - waterboarding is a remarkably shitty thing to do to someone, and it's a spectacularly shitty thing to do to someone who's innocent of any crime. Torture proponents always bring up the "Jack Bauer scenario": would you waterboard someone in order to prevent a nuclear attack on Los Angeles? Thankfully, nuclear attacks on major American cities are still theoretical, but sweeping the innocent up in anti-terror sweeps isn't. It's something I always ask people to bear in mind when they're forming their opinion on torture: much like the death penalty, this shit is happening to innocent people. Right now.