Maybe you misinterpretted what I said about a menu, you can have a multiple select menubox rather than a drop down menu.
But, I wont go into too great detail, becuase I just happened to read this...
There could be as many as 500 rows in the drop down menu - I want to send two columns, selected from the drop down menu, with each form submit.
500 rows?
And you expect a user to sit there and scroll through that?
There's a concept that I really fight it out tooth and nail with sometimes with clients, and that's called user experience.
Imagine yourself as a user faced with a drop down menu of ~500 items. Personally, I'd just laugh and click the hell out of there pronto.