tar -xvf filename.tar will un-tar a tar file. The j flag to tar in Linux pipes a .tar.bz2 file through bunzip2. And I think the f flag has to come last, because tar looks for a filename as an argument to the f flag. x is for extract, v is for verbose, f is for filename.

Winzip should also open .tar files, from what I remember. Any archival program worth anything will be able to un-tar a tar file.