I am a moderate Highlander fan. I used to run a GURPS campaign in the CompuServe Roleplaying Games Forum, based on Highlander. I now run it on the Dreamlyrics forum. It doesn't use any of the characters from the movies or TV series-- no Duncan or Connor Macleod, no Kurgan, etc. Each player character's story is set in a different time and place. I have done considerable historical research in the course of running this game, and it's one of my all-time favorites.
Amadán's GURPS Highlander Rules
(You can also download them as a zipped Word file or in plain ASCII text (also zipped).
There are several other sets of unofficial GURPS Highlander rules out there:
As well as the famous "Highlander: The Gathering" netrules for use with White Wolf's World of Darkness.