ok I'll try it:
Here for winXP:
Open the windows (file)explorer.
Navigate to your zipfile.
Double click on it.
Now you should see the content of the zipfile.
mark all the files/folders you see there
press ctrl-c
navigate to your glest installation dir ( with fileexplorer ).
( typical c:\Program Files\glest2.0.0\ )
press ctrl-v