Cannot publish new .htm file with Contribute

A client of mine is having an issue with a webpage he maintains daily using the Contribute package, and one major problem has come up while trying to add new features to his presentation. Instead of linking directly to a file as has been done in the past, his primary web designer has created a new pop-up style (on demand) window that presents video in one portion and an advertisement in the rest. Unfortunately, this option did not come with an associated template - he merely configured the page to link to a .txt file as Contribute would not let the user (Administrator) upload a new .htm file.

My question if anyone might have a few moments to respond, is whether or not this is a feasible thing to manage? .txt files work in Internet Explorer browsers, but fail on more standards compliant options such as Firefox or Apple's Safari (3.0 beta tested on PC, other versions tested on MacOS X) in which case they merely result in the presentation of a plaintext file in a pop-up window.

Can a new template be created in Contribute, and files generated from this? Is this a technical quick-fix situation, or a more involved problem that requires Dreamweaver or other template creation options?

Sorry to be rather vague on this one, it's a particularly complex situation (with a bit of a time crunch) on the user end, and I'm hoping to track down any information I can.

- J. Johnston