A good way to get started would be here:
J2SE[tm] 5.0 in a Nutshell
http://java.sun.com/developer/technicalArticles/releases/j2se15/
New Language Features for Ease of Development...
http://java.sun.com/features/2003/05/bloch_qa.html
This blog entry has a 'See Also' section at the end. Have a look at those references as well.
After that, drill down from the main product documentation page:
http://java.sun.com/j2se/1.5.0/docs/index.html
For example, New Features and Enhancements
http://java.sun.com/j2se/1.5.0/docs/relnotes/features.html
There are also many articles in the trade magazines. Try searching for
Java tiger new features on your favorite search engine.
Hope this helps.
"Troubleshooting Guide for J2SE 5.0",
http://java.sun.com/j2se/1.5/pdf/jdk50_ts_guide.pdf