I have been using 7-Zip as a compression utility for a long time now. No more troubling with WinZip or WinRAR, both of which have distinct disadvantages: WinZip is a run-all-the-time resource hog while WinRAR is proprietary and non-free. 7-Zip runs all the usual compression algorithms in both directions plus adds functionality for the new 7z compression format.
In Windows 7-Zip also adds context menu (right-click) functionality for compression and decompression actions. The thing is I was having trouble getting that functionality to function on my Windows 7 machine. Turns out I had made a simple (and easy) mistake.
They make both a 32 and 64 bit version of 7-Zip. The 32 bit version works just fine on a 64 bit Windows machine. However, the 32 and 64 bit architectures of Windows make different use of the context menu; in short they are done in a different manner. So, even though the application seemed to be working perfectly the context menu information was (presumably) erroring out behind the scenes.
No big thing. Just uninstall the 32 bit version and install the 64 bit version (third link down currently). Voila! Context menu options.
Have fun with that.