well tae kwon do literally means to crush with the foot or something like that my korean is a bit rusty...meaning i dont know any korean cept that karate is more about punching and chopping and kick boxing well its boxing with a bit of kicking thrown in they all have similarities but most of it comes down to the technical aspects...the chambers forms and things like that as for the second question it all depends on the persons skill level and not their style of choice =op
Karate is different from Taekwondo and Kickboxing in a sense that Karate is a more complete fighting system. It is mainly a striking art but it has a beautiful balance of utilization of both arms and legs. It doesn't discrimminate and focuses only on one aspect. Like in Taekwondo they only focus on kicking techniques and in kickboxing the punching is emphasized more.
Of course a kickboxer or a taekwondo fighter can beat a muay thai or karate fighter. It is more about the practioner than the art itself. A really good kickboxer or a taekwondo guy could easily beat a sucky and horrible muay thai or karate fighter.