Changes in AASHTO?

[tngolfer]

My office has the AASHTO Standard Specs. for Highway Bridges 2002 and the brand new 2007 (w/ 2008 revisions). Since we are a structural firm they won't buy every version of the AASHTO code. Unfortunately, 4 of us younger engineers will be taking the SE1 this year in which 20% of the exam refers to the 2004 code (w/ 2005 and 2006 revisions).

My questions to the transportation group are:

1. Is the 2004/5/6 AASHTO code more similar to the 2002 or 2007/8 code? Which should I use to study?
3. Are there any major changes I should know about?

Thanks for any help you can provide