Looking at the forum archives, I see a few other people have had this problem, but I don't think anybody came up with a solution, so I'm going to describe my problem as completely as I can:
I'm currently moving my MovableType site over to DreamHost. When I tried to log in, I discovered that the usernames all disappeared. Checking the MT docs, I found this:
http://www.movabletype.org/docs/mtmanual_troubleshooting.html#i keep getting the movable type login screen
Apparently the solution is to dump the database files into text format on my old host, move them over to DreamHost, and re-load the text files into database files. My old host doesn't have db_dump; the closest I could find was db33_dump (I presume this is version 3.3). I did this on all my MT files and moved them to DreamHost.
When I try using db_load on DreamHost, though, I get this message:
db_load: unknown input-file header configuration keyword
Looking at /usr/bin, I see there's a "db3_load" program. I converted my files back using that, but MT still doesn't seem to work, so apparently that's not what I need to do.
I still have access to my old host (for now!). Does anybody know what I need to do here?