There aren't any huge changes between 5 & 6. I think that for the most part, if you're going to jump in the SCJP pond, you may as well go for SCJP 6.0.
There is the K&B SCJP certification guide that is the standard, and it has been updated for SCJP6. It's a great resource. I'm working on a book of mock exam questions myself which is due out around the end of summer or fall. Some sample questions are on my blog so feel free to check them out: [
If you have some old SCJP 5.0 resources around, I'd say there's no need to buy the SCJP 6.0 resources. Just do the exercises and samples in the book with a version 1.6 JVM and you'll do fine. I doubt you'll find too many differences!
In general anybody who is in this forum says that there is not much difference between the two, and I personally think that should go for scjp 6 since it's the newest and I am going for it too(I was also in this dilemma a little while ago, refer here this person passed the test and also tells about his experience [ July 20, 2008: Message edited by: vaibhav mishra ]