What to do with a user created by import-mt?

I successfully imported my old MT entries, and in the process a new user was created. But I have no idea what that user’s password is, and I’m not sure how to set that user’s password when I’m logged in as admin.
What I really want to do is assign all those posts to my admin user so I don’t have to use a superfluous second user. Is that possible? I’m willing to get down-n-dirty with the DB…