Alister,
The basics are pretty similar although there were some new syntax changes introduced over time. Java 6 is a lot more powerful (more libraries, more features) though so I recommend a good recent book to pick up on the new stuff.
I agree with what Jeanne said, but as far as additional learning areas... the big ones I would focus on or at least familiarize yourself with are the XML apis, the collections apis, and Swing.
I would also highly recommend browsing through the JavaDocs in detail... it may sound like reading a dictionary, but you can often find things you never knew existed... and also you will have a better understanding of what the Java library provides by default.