Set up the Java Development Kit
Download the JDK (J2SE 5.0): Go to this web page: http://java.sun.com/j2se/1.5.0/download.jsp and click on "Download JDK 5.0 Update 4" (it should be near the top of the page). On the next page that appears, choose the "Windows Offline Installation" link (probably the first file). This is a large (about 50 megabyte) file. Save the file to your desktop.
Once the file has downloaded, double-click on the icon on your desktop (it will be called something like "jdk-1_5_0_04-windows-i586-p.exe"). Follow the instructions to install the program (you mostly just have to click on the "Next" buttons).
The installation program will install the Java development kit into a folder on your hard drive; most probably: "C:\Program Files\Java\jdk1.5.0_04". Go to your "My Computer" icon, open it, then open the C: drive and see if you can find the jdk1.5.0-04 folder listed in the previous sentence.
Now, using your mouse, right-click on the "My Computer" icon, and choose "Properties" at the bottom of the pop-up menu that appears.
Click on the "Advanced" tab. Then click on the "Environment Variables" button.
At the top of the dialog box that appears, in the "User Variables" section, see if a "PATH" or "CLASSPATH" variable is listed.
If "PATH" is listed, select it and click the "Edit" button. If there is no "PATH" listed, click the "New" button - enter PATH for the variable name. for the value of the PATH variable, put: C:\Program Files\Java\jdk1.5.0_04\bin (If there are other things already listed in the PATH variable value, then type the new value at the end of those, after adding a ";" (semi-colon) to separate it from anything that's already there.) Click "OK" when you're done.
Similarly, for the CLASSPATH variable, click the "New" button and enter CLASSPATH for the variable name. For the value, type in: C:\Program Files\Java\jdk1.5.0_04\jre\lib\rt.jar;\. (notice the extra symbols at the end of that line ";\."). Click OK when done.
Click "OK" to close the Environment Variables box. Then click "OK" to close the "System Properties" box.
Set up the DrJava editor
Go to www.drjava.org and download the Current Stable Release (click on the "Download Windows App" button). Save the file to your desktop. You may rename the file to "DrJava" if you want.
To run DrJava, just double click on the file. The first time you run the program, it may ask you to find the "tools.jar" file. Click on the "Yes" button and find the tools.jar file in the C:\Program Files\Java\jdk1.5.0_04\lib folder on your hard drive.