locking to domain

Hey all, I have a rather simple need that I am sure a lot of you must have gone through, I need a bit of code so that the script can run only at "something.com"..I am generating a MD5 license "key" based on that... Problem that I am having is.. wont I need 2 "keys" to see if the domain is with a "www" (eg www.something.com) or is being run without the "www" (eg: http://something.com) ? I'm pretty sure it can be done with one key....but how? I tried google with http://www.google.com/search?q=php+locking+script+to+domain&hl=en&lr=&ie=UTF-8&oe=utf-8&start=10&sa=N and even hotscripts.com and the other search results without any success... anybody have this handy bit of code I could borrow? :-) Thanks, -Ryan