It is possible that the files have been zipped with a recent version of WinZip - a new format (Zipx) was added at V14 in May 2009. Since that is the default format for new achives (grrrrr!) it is quite possible that the archives are formated with that, and you cannot read them.
If you go to
WinZip[
^] you can download a trial version - it nags you to buy it and register IIRC, but is otherwise complete.