Flaharty
Are you using the 64bit version of Vista?
If so, older versions of Winzip do not support the right click context menu items. Make sure you have the latest release of Winzip.
If this is the 32bit version, make sure you have the latest version of Winzip and try reinstalling.
Also, check the following website for more information on enabling this context menu.
Toggle WinZip's Context Menu Additions:
http://malektips.com/wz0037.html
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Ronnie Vernon
Microsoft MVP
Windows Desktop Experience