If you already have Java Development Kit on your PC and the bin directory is in your path (in most cases), you can use the command line:
jar xf test.zip
or if not in your path:
C:\Java\jdk1.6.0_03\bin>jar xf test.zip
Complete set of options for the jar tool available here.
Examples:
Extract jar file
jar x[v]f jarfile [inputfiles] [-Joption]
jar x[v] [inputfiles] [-Joption]