It actually depends on the server set up if 755 would work or not. So hard to say overall. That's why X-cart creates catalog directory with 777 permissions.
So to put html catalog in root, would be best if a copy script were run or something like what Jared suggested. Or go in and chmod to 777 then back to 755 after done. But if you generate your catalog as often as I do, you wouldn't want to do that every time.
Carrie