It was created a java package called "FreeModbus.Util" that contain a modbus class that can be used to comunicate directly with Modbus/TCP slaves connected in a TCP/IP network or you can use a TCP/IP - Serial port interface as explained in Configuring TCP Server.
Install a http server in your computer, there are some freeware http servers. You can find some at www.tucows.com.
When extracting the source code you will find a directory called java\ModbusMonitor. This directory contain the java applet sample that must be called from "ModbusMonitor.html" html page.
Configure you http server to have access to directory mentioneted above and create an alias for this directory , for instance, /Modbus . You do not need two computers to test the applet, use your http server at loopback IP address 127.0.0.1.
Configure the modbus server as explained in Configuring TCP Server ( TCP/IP - Serial port interface ). It's important that http server and this modbus server use the same IP address.
Now , if http server and Modbus TCP Server are working you can try the applet. Start your browser, IE or Netscape, and type http://127.0.0.1/Modbus/ModbusMonitor.htm (This is valid if you use IP Address 127.0.0.1 , and use /Modbus for installation directory alias). Now , you can read and write modbus regs and coils.