I went through the program in 2007 in Boulder (the first year they were offering it) with Brightkite.
I'd definitely recommend doing it, it's more than worth it. To answer your specific questions:
a) It's primarily about the team. Assemble a founding team that has a history/evidence of being able to execute. You can do that by either having an impressive resume, or (in my case back at the time) demoing software that you've written, even if it's not directly related to what you're applying with.
There are also a bunch of online resources that answer this question. A select few:
http://nattyzola.com/7-pieces-of-advice-to-techstar-applican...
http://www.seattle20.com/blog/Some-tips-for-applying-and-get...
http://www.nearlynicole.com/2010/05/tips-for-applying-to-tec...
b) This really depends on your experience, but in a nutshell, try to focus on learning the things you have little experience in. For example, if you are a great engineer, but know little about raising money, focus most of your time on that.
Also, my friend Jon from IntenseDebate (sold to Automattic) has some great advice here:
http://jonefox.com/blog/2008/06/08/tips-for-techstars-teams/
Hope this helps,
Martin