How do I prepare for Developer Training in Denver?
I'm going to be starting here at the developer wiki - http://wiki.civicrm.org/confluence/display/CRMDOC/Develop 

and continuing here - 
http://wiki.civicrm.org/confluence/display/CRMDOC/GitHub+for+CiviCRM

and I might just buy the book here, though it may be out of date- http://www.amazon.com/Using-CiviCRM-Joseph-Murray/dp/1849512264