The way I plan to do my forum, the thread links will, if Javascript is not enabled, simply link to a new page that the server will render, in effect working like a regular non-AJAX page.
Fortunately both the AJAXy page and the static version both get sourced from the same post template, but even so it's still duplicating a lot of stuff so it's hardly optimal.
And thanks! Although I suspect a lot of that speed is down to the fact there's only about 6 threads, 6 users and 100 posts :D Whether it's still fast with a DB the size of Teh's, and the traffic to match, remains to be seen.
EDITED: 3 Nov 2010 19:41 by CAER