Hi
The message you are getting could be because of two things. You have to register Editor, and then you have to use the Options menu in Editor to enter the serial number you have been sent - this will turn off any warning messages and remove the five-screen limit.
The other possibility is that you have changed Editor using Options -> Preferences to behave like the Professional and Developer Edition. If this is the case the the restrictions will come back into force if you have only entered a free serial number. The aim is to allow anyone to try out the commercial versions for as long as they wish.
So the answer is to make sur you have entered the serial number and make sure it is switched to behave like the free edition.
As for the question of what the differences between the editions are, you can see this here, in a table:
http://www.questiontools.com/prodeditortable.html
Hope this helps.
Regards
Paul Booth
Question Tools Support