I took an idea from another forum about changing the type from "submit" to "button", and used onlclick="window_open()" to just open the new file. It works in IE6-8, and the last couple of versions of Firefox/Safari/Opera (we have clients with older GIS/database software that require older browsers and older versions of java to function).
The first button above uses a simple window.open() command attached to a button (not submit), without linking to another function located anywhere on the site (on the web page, JQuery, or other js scripts).
The second button uses the native Thickbox/JQuery tb_remove() function to close the window if they dissagree. The native "close window" command at the top of thickbox modal window allows them to close the modal window after they download the file.
Since I’m trying to get the user to download a zip file, the OS-based "Save/Open" automatically window pops up whenever you link directly to the zip file.
I know that this is sloppy, but it seems to work. Any reasons why I should not use it? I would prefer to do a straight-up asp page hooked to a database, but was over-ruled by my boss (pop-up blocking issues, they WANT a modal content window).