There are two version of the code.
If you want to download the plug-in and use that in your website without change anything. You could use this version:
You could also get the full code with comments explain almost everything in there.
10/03/2009 - Groject-ImageSwitch 1.0.0 - Compressed Version
17/03/2009 - Groject-ImageSwitch 1.0.1 - Compressed Version