It's simple--if you want a zip file instead of the cbz file, just highlight the file, right-click and chose "Rename," and then rename the extension to zip instead of cbz. You, of course, have to have the Windows settings so they're showing your file extensions. The file Superbook_01.cbz would be renamed to Superbook_01.zip if you've renamed it correctly. A little box will pop up a warning when you change it, just hit the okay to change it anyway. You can then open the zip normally and extract all the jpgs.
I just did this to repair the Eh! 5 book. Once I renamed it from cbz to zip, I unzipped it, went into the jpgs and used the Windows Paint program to 180 degree rotate all the upside-down jpgs to the right direction and saved them that way. I then re-zipped the file including the fixed jpgs, added "fixed" to the name and changed the extension back to cbz. I uploaded it, and this is now the file on the site for that book.
If you come across cbr comic files, simply rename their extension to rar and extract them with a normal rar extracting program to get the jpgs.
Hope this helps,
Shane