Copy RXTXcomm.jar to the folder c:\program files\java\jre-version\lib\ext
Copy rxtxSerial.dll to the folder c:\program files\java\jre-version\bin

jre-version is the version of your java (jre6, ...)

Replace all occurences of import javax.comm.*; with import gnu.io.*; (in the SerialPortCommunications class for example)