I have upgraded the website to Movable Type 2.64 and implemented a comment anti-spam feature. I tested it, and it seems to be working fine, so let me know if you run into any problems.

I had been running 2.51, but the anti-spam plugin requires 2.6 or better so I had to upgrade. I don't see anything really all that new with Movable Type, so I don't think I missed much by not upgrading sooner. I only upgrade to get new features, not just for the sake of upgrading like many people.