Upgraded Movable Type from version 3.11 to 3.15. Downloaded just the "upgrade distribution file" rather than the full distribution. Since my PowerBook is now my blog server, using the Mac's Finder, I just opened up my mt folder and the MT-3.15-upgrade-en_US folder, selected all files in the 3.15 folder except the extlib folder, and dragged and dropped the 3.15 files into the mt folder, replacing the old-version files. I then I opened both extlib folders and dragged and dropped all the 3.15 files into the installed extlib folder, replacing. My existing extlib folder contained additional "external libraries" that I had added earlier so this is why the extlib folder had to be updated that way (as per the upgrade instructions). Then I did a full rebuild of the site.
Just finished migrating this (Perl-based) Movable Type blog and our (PHP-based) photo gallery over from a Linux-based server in the US (web-hosting service) to this very laptop I'm typing on right now at home — an old PowerBook G4/500MHz (Titanium) running Mac OS X Server 10.3.7. This PowerBook is connected via an 11Mbps 802.11b wireless connection to my D-Link wireless access point, ZyXEL Prestige 314 broadband router, and then through to a 6Mbps DSL broadband connection from PCCW Netvigator. Took like 3-4 weeks(!) to do but I learned a lot in the process. As it's almost 3am here now, more later on this later as I'm off to hit the sack!