Website works on one server, not another

I'm working on a client's website. It's worked fine on our test server but when we moved it over to his server this weekend, it started acting up as seen here.

Depending on what OS and browser combination you use* (see below), either the pages show up as actual HTML code (rather than a "normal" website) or the pages display properly but the javascript, rollovers, and server-side include don't work. I'm positive this has something to do with the client's server as it was working flawlessly before it was moved from ours to theirs. Could their server not be able to handle javascript for some reason? In all the sites I've designed, I've never seen anything like this.

*In general, it seems like the website displays properly in IE but the rollovers and include don't work. In Firefox, the site shows up as all HTML text.

m19