Opening .SIT files...
 

How can I open a .sit (mac file) using a PC?
I heard there is a tool, but forgot the name.

.sit files are compressed Stuff it files.

do a search on "stuff it" on google.com

Stuffit is a cross-platform compression format by a third party. Not particularly a Mac thing, though I suppose mac users do use it more than zip.

Anyhow, it's by Aladdin:
http://www.aladdinsys.com/
Downloadi it for free.