There are a few things you should do in order to be ready for the class.

1. Ensure you have a CUNIX account. It's preferable (although not absolutely required) that you have an "extended instructional" account, as it has fewer limitations as to what you can do on CUNIX. See http://www.columbia.edu/acis/accounts/Student_Accounts.html for more details.
2. Make sure you can log onto newcunix.cc.columbia.edu; this is the new computing cluster capable of running the latest version of Java. Note that you cannot telnet to newcunix; you must use a secure telnet-like protocol called ssh. If you want the ability to ssh from a Windows box at home, you can use a free tool like Teraterm Pro (http://www.columbia.edu/acis/software/teraterm/) or PuTTY (http://www.chiark.greenend.org.uk/~sgtatham/putty/).
3. Write, compile, and run a test "hello world" program in Java. (This exercise is left to the reader.)

That's it! Once you've done the above, you're ready to develop on the CUNIX cluster. You do not have to, however; I've assembled a resources page (http://www.columbia.edu/~cs3134/resources.html) that has links to Windows development tools. However, you will be expected to test your code on newcunix, as we will be grading it there. If you have problems, visit one of your TAs ASAP; the first few weeks are a perfect opportunity to meet them during office hours and make sure you're off the ground and running, as you won't have time later in the semester to debug account and Java issues.