When I finally got around to upgrading Movable Type to version 4, the custom templates I had been using reached breaking point. The comments pages were on their last legs and I had to disable comment previewing.
Now, after another upgrade to the last release of MT4, I've given the blog a new design. It's even more minimal a design than the last one but I've kept the narrow format of the previous version. Hope you like it.
I think the problem that was slowing down the comments script has also now been fixed.