For instance, if I wanted to zip everything in My Documents, but not subfolders in My Documents, and I also did not know the name of each subfolder.
Open a command prompt and if 7-Zip is not in your path, navigate to the directory with the 7-Zip files, then type:
This just zips all in files in documents but not any subfolders.
If you are using a Pre-Vista Windows, the example above may not work unless you have a 'documents' folder in your home directory.
The 7-Zip help file has examples for all the command line options.