There will be a 2.9 release soon which will be more or less a 3.0 beta. The latest developer versions can be obtained from www.limewire.org. Simply get a cvs client (WinCVS or something), the latest Java Development Kit (from www.sun.com - usually a user will not install the JDK but the JRE because it is smaller) and ant from ant.apache.org.

There are compile and run scripts in the source code that will take of everything else.