cant open .zip file on CD

Some time ago I backed up some photos on a CD from my XP machine. Now when I try to view these on my new Vista PC it keeps asking for Lumix simple Viewer which I no longer have. These photos are zipped but I don't know where in Vista to find a program to unzip the files. I can do it on my laptop which still uses XP, there is a wizard which extracted the photos and I now have them on the hard drive but I want them on my PC. Do I have to buy a non Microsoft program?