Maybe a CSS problem? The WWWThreads output is pretty CSS-dependent, and sometimes that can produce unreadable pages for browsers that don't implement CSS correctly. Do you know what WebTV version they are using? Original ("Classic"), WebTV Plus, etc?
There used to be a WebTV emulator that you could use to see what WebTV viewers are seeing when they visit your site. I'm not sure if that is still available or not, you might want to check.
