Unzip xplanet-1.3.0.zip on your desktop to create an xplanet-1.3.0 folder. A description of the files in the zip archive is in windows.txt. The included batch file xplanet.bat has some sample commands you can run to see how xplanet works. If you get an error saying you don't have permission to write the desktop file, use the -tmpdir option to put this file somewhere else:
The option "-tmpdir ." means put the intermediate image in the current folder. A day and night map of the earth are included. Other planetary images can be found by following the links on the main Xplanet page.
I don't have much experience programming on Windows, but if you have any problems, please let me know and I will have a look. When sending a bug report, please describe the way to reproduce your problem. The more information I have, the more likely it is that I can help you. At a minimum, run xplanet inside a DOS window and tell me what happens.
Thanks to Nigel Stewart for much help getting Xplanet to run on Windows in the first place.