Dave,
go get the "Airline Techinical Interviews" book and the "Knock em Dead" interview book (available at kinko's). Those two books will not do you wrong. Keep in mind, each question they ask is done with the intent to uncover a personality trait. The "Knock Em Dead" book exposes what they are looking for. If they want to know about a time you made a huge mistake, don't tell them about landing on the Wrong runway in Corpus, tell them about the time you got caught up talking with your friends and walked out of a resturaunt without paying, and how you immediately went back in to make it right. Turn negatives into positives and try to avoid telling them how crappy of a pilot you are (and yes, we've all made HUGE mistakes in the jet...)
You'll do great. It's easy for us on the inside to say that, but the quality guys tend to rise to the top. Now why you want to fly for UAL at the current rates...that's another story. BTW, where did you fly before to have got that unique mix of experience (looks like UAL except for the 321s...)?