Ok, moving from a "conventional" movable type installation to a "MySQL" MT installation is officially now a major hairy pain in the ass. What follows will make sense only to those relatively fluent in the SQL database language. Those who are not: in my experience, there is a significant bug in the import process to do this conversion. I was importing entries at about 100 per pass. Each pass required zortching the successful entries, and re-uploading the rest. Each upload took about 4 minutes. Big deal you say? We got 10000 entries and comments!
How I solved it is below...
PS... email this entry is still broken... working on it...
MT-Entries has the mt-entry-author field set not to allow NULL. This is normally a Very Good Thing, as nulls cause all sorts of headaches when running queries. Unfortunately, it would appear that a bug causes the import process to hand a NULL value in this field to this table, on irregular occasion. For the life of me I could not figure out where or why, and I'm sorry pouring through a 10k entry dbase backup looking for a single null is beyond my abilities (and probably wordpad & notepad's too). Those of you with shell access and the ability to run regexes through bash or whatever will probably smirk, but I did what I had to do.
At any rate, by changing the mt-entry-author field to allow nulls, everything imported just peachy. When I was done, I ended up with, oh, two dozen or so bizzare entries in the STORIES area, and a whole bunch of errors besides. Zapping these fixed everything, and now it all seems (seems) to be working fine.
So props to Hosting Matters for giving me the ability to directly tinker with mySql databases. Otherwise I'd've been here all frikkin night.
Anyone else wants to do this I'm happy to help, but you'll owe me a case of beer in the morning!