Bshugg wrote this simple and easy to follow

Step by Step Guide

Here’s how to get the DnD mini program running:

First off buy as much DnD minis as you can. It’s a great game. If I hear of anyone playing on the server who is playing with “pirated” stats, then I will do my best to keep people from playing you. This is a free program, but the game is NOT free. If you like it support it!
In order to get the program running for DnD minis, you need to download and install 3 files. One of these is a .zip file which is a shrunk down file. If you don’t have a unzipping program you can get one here:
http://www.winzip.com/
get the evaluation version and its free.

Once you have that then you need to get these three things:
1. Java runtime environment
2. Vassal engine
3. DnD skirmish module for the vassal engine

1. Java runtime
Java runtime is a program that allows you to run programs written in java on your PC. I suppose you could get this from the java/sun website, but this method listed below will set up an auto install.
-Go to this site:
http://www.vassalengine.org/
- click the download tab on the top right, when a new window comes up with downloads you should see a statement that says:
------------------------------------------------------------------------------------------
Latest version: X.X.X.X
Release Date: XX. X, 200X
Click here to launch VASSAL
If you have problems, read the notes about using Web Start
------------------------------------------------------------------------------

To get the java runtime click on the underlined word “notes” in the bottom sentence. This should bring up a page that says:
------------------------------------------------------------------------------
VASSAL uses Sun's Java Web Start technology to launch. Web Start is packaged with version 1.4 of the Java Runtime Environment (JRE), which may be downloaded here. If your platform doesn't support Java 1.4, you can still run an archived version of VASSAL.
-----------------------------------------------------------------------------------

- click on the underlined “here” in the text and that will take you to the java runtime page. Click on the download box (its green and on the right) and select what version of windows you are running. It should then proceed to auto install. You may have to answer a few questions. It will pop up a box saying something about a program trying to get “unauthorized access” to your computer. Click ok. Its just trying to install something that can access your computer’s kernal. Normally this is a bad thing, but its ok from this site, and it only does it once. It won’t be able to access your kernel after the download and its NOT a virus or anything.

2. Vassal engine
The vassal engine is a java based program that allows you to run various mini or board games. It’s a generic program with features like turn tracking and die rolling. The actual DnD stuff is located in the DnD skirmish module below. You have to have this program to run the module.
Back on this site:
http://www.vassalengine.org/
you can download the vassal engine. Its in the downloads area. Download it then click on the icon for the file (REMEMBER WHERE YOU DOWNLOADED IT TO!) to install it. It should do some more downloading.

3. DnD mini Module
This module contains the graphics for DnD minis, a board , and things like spell templates. It doesn’t contain any rule info.
you can get the module from any of these sites(if you know another or a link is broken, email me):
http://www.lemonbutter.com/dd

Once you get the file there is another step. Its stored as a .zip file that you need to unzip. Winzip unzips files into a folder on your C drive called unzipped. Check there if your using winzip. Move all the files to the location you have put vassal in.
Now you should be able to open up vassal and click load module. Load the rpgskirmish module and you should be set. Once on the program a window pops up with some tabs like Tiles/Units and 1d20. click on the icon that looks like this:
---->
< ---

it should bring up another split screen on the right. This is the chat screen Click on the 2 arrows icon (like the one above) on the right side (in the chat screen) to connect to the server. It should say over in the text box something about connecting to the vassal server.

Once you are on the server:
There will be a list of active rooms where you will start in the Main room. You can right click on a room name to join it, or create your own name.
To watch a game in an active room right click on a players name and choose “synchronize”. This sync’s you to the players and allows you to see the board.

If you have any more specific questions you can PM me at the wizard forums (bshugg) or email me at bshugg@hotmail.com. Enjoy!

To get more help read these files:
Readme
RPG Skirmish Game Basics