It would appear I just wasn't looking properly, as I have now found a list of several scripts, including phpMyID. So, I should soon be able to log into all websites with "http://nathan.jones.id.au".
Of course, by "log into all websites", I really mean "log into all 2 of the sites I use that support OpenID".
Come on Wordpress! (I'm not holding my breath on OpenID adoption by MySpace or Facebook!)
Edited To Add: It's tempting to set it up whilst I wait for Theresa to return, but I really, really should finish up this bloody newsletter. Never get volunteered to do a newsletter - even if they give you the content - unless you do desktop publishing every day.