Unfortunately the article didn't help me, probably because I'd been an idiot and deleted the mm5 folder.
Anyway, I sent a mail to dreamhost and said I'd deleted it. They replied the next day that in that case they'd actually have to contact Miva and request a new key for me. They did so, and mailed me the next day and told me now it's fixed, go ahead with the installation.
If you do like me and delete the mm5 folder, the only way to correct it is through support....So DON'T DELETE!
Sorry I can't be of any help to the others, but can give a warning at least.