Hi, i was curious if it was possible to compare and verify a url.

here is the circumstance

i have a link on my social site to ajax im (it runs on a dif database that i own)

when the window opens i want to verify that the originating click came from my site link.  if it did not then i want to pull up a screen that says sorry but you must be a member to use this service.   (they cannot access the link unless they are a member now)

so to restate..  

a member of the social site clicks on "IM"   they are taken to the IM window and all is well.
a non member of the social site pulls up the im window by its direct link manually  example www.xxxxx.com/im.html - a window opens that says sorry you must be a member of this social site to use this IM

is it possible to compare and check the orig path and make a switch...