You will need to set up a CS Unix and a CS Windows account. You can do so by going to the undergraduate CS lab and following the instructions (they are taped on the walls and next to the computers, if you are not sure what to do ask the attendant). There are only Windows machines in the instructional lab (where we have our lab sessions), so you will need a Windows account in order to participate.
In order to submit the homework, you will need to use WebCT, which requires a kerberos username/password to log in. If you do not have one, you will need to go to the undergraduate CAS lab (basement of MCS building at 111 Cummington Street) to set it up.
You can download Eclipse on your own computer if you prefer to work on the assignments at home. Eclipse is a development environment (what people call an IDE: integrative development environment) which comes with the java software necessary to compile and run programs (sdk: software development kit to create the executable, and jre: java runtime environment to run the executable). Alternately, you can download the java software from the Sun website and use your favorite development environment (such as NetBeans, provided by Sun, or a simple code editor). You can find the links for these resources on the Desription page.