To work from home on a Windows computer you should

1. Download Java from Sun's download page.  You want to click the "download" button next to "JDK 6". You will then click the "accept license agreement" button and then (depending on you computer) probably select the "Windows Online Installation, Multi-Language" link.
2. Execute the downloaed file which will install Java (and it may take a while).
3. Download BlueJ from the bluej home page. You will want the bluejsetup-213.exe file
4. Execute the file just downloaed. This will install BlueJ on your machine.