If you use Mac OS X or some flavor of Linux, you already have the means to ssh in. Please see the SSH FAQ listings.
To ssh to the Linux machines with Windows (7, Vista or XP) we recommend installing an ssh client such as putty, a free download. This will only provide command line access. You can also try Cygwin which is available free online. CygwinX provides an xserver, allowing you to open X windows (GUIs, java, etc.), but see the next paragraph for the best option.
The recommended way to connect to our Linux machines is NoMachine. This provides a full GUI login, as though you were logging in to the machine in the lab.
See also which machines you can connect to here.