If you need to understand DB2 licensing, there is an excellent series of articles on IBM Developerworks written by Paul C. Zikopoulos. I made following table to help you easily find information you need.
|Choose DB2 version||read||read||read|
|Compare DB2 versions||read||read|
Take a look at PVU pricing and DB2, current PVU table and DB2 subcapacity licensing, subcapacity licensing faq and software licensing in virtualized environment. If you use mainframe, take a look at Choosing DB2 Connect version.