New to Java

So, I've been chosen to teach some Java classes where I work.
My only qualifications are writing in C for about 20 years and Java for the past 5 years.
Oh yeah, I once taught some UNIX classes that seem to have been well received.
The one advantage I have is the relaxed atmosphere - most of the people who will be attending are people I know and with whom I've been working.
But teaching Java is a horse of a different color.
I would appreciate any suggestions anyone may have - what to mention briefly, what to emphasize, what to ignore, what preparations I should make.