For Ace files, use WinAce For sit files: Let them be, DON'T get that stuffit expander unless you want to screw up a lot of things. This thing associates itself with all sorts of files and is hard to get rid of again.

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.