I want a second events calendar but I have not tried Theo’s calendar hack. I’m wondering if I can’t make a duplicate copy of all necessary calendar files and just rename them (calendar.fns.php and calendar2.fns.php, for example)? I realize that I would also need separate data in the database.

It’s not a matter of renaming the file, but rather duplicating and renaming the functions contained within the file.  You’d also have to hack it to point to the new database tables.

It seems to me that Theo’s Calendar add-on would be much easier to use.