How did mystery science theater get away with using old videos legaly?

Question

and, is it legal to use current tv or video in the same way? Weird question I know, but its something that I wonder.

Answer 1

MST got permission.  Just about every old show or movie will sell you permission for a price -- after all, they were produced to make money.  You can buy permission for new shows also -- but it's very very expensive.  The older the show, the cheaper it gets, but the famous old ones will still cost a lot.