You don't need MS Office to unzip files. You can download free unzippers at
www.pkzip.com .
I have seen most of the GMAT+ things that are floating around, and I think you'll be very disappointed when you see them. They are merely bad photocopies of bad printings of questions. There are many typos and incorrect answers. And much of the stuff that people sell comes from the downdowndown.net site. It's up to you, though!