No, that's not Kirk squaring off against his transporter duplicate: It's a scene from William Shatner's Spaghetti Western, White Comanche. A new DVD set is full of Trek stars' cowboys-and-Indians adventures, which really feel like lost Star Trek episodes.
Honestly, it's better than the episode where Shatner goes around screaming "I am Kirrok!"
This film, in which Shatner faces his doppleganger once and for all, and also consumes some peyote, is just one of the great films on the new DVD box set Trek Stars Go West. There are also TV episodes featuring DeForest Kelley (in The Lone Ranger), Leonard Nimoy as a Comanche, and James Doohan sporting a crazy wig in Last Of The Mohicans:
The DVD box set comes out on November 9. More too-insane-for-words clips at the link. [Trek Movie]