This site should help you to decompress a .sit file, the Mac equivalent of a .zip file, in Windows. http://www.stuffit.com/win/expander/index.html
I am helping out a friend who sent some files from his Mac to his PC before he erased his Mac hard-drive. The files were word .docs and came into his PC as .sit files which his PC cannot open.
What is the best and easiest way to convert these .sit extensions to .doc or .zip (Winzip)?