The system requires a reasonably recent (i.e., from 2000 on) Java-enabled browser. Below is a list of browsers which have been tested and are known to work (later versions can be presumed to work also):
Windows
Macintosh
Linux
If you are using a variant of Windows, then you will get the best results with Sun's Java Runtime Environment, available from http://java.sun.com/javase/downloads/index.jsp - download 'Java Runtime Environment (JRE) 6 Update 2' - although it should work without it with any of the above browsers. If you are using the Macintosh with MacOS 9.2 or earlier (i.e., not OS X), you should be using the Macintosh Runtime for Java. (If you are using Mac OS X, this does not apply).