My PHP OpenID consumer is working!
This will be out as open source fairly soon. The only binary libraries it needs are either gmp or bcmath. It seems that at least one of these is usually installed with PHP - I have bcmath on my development machine and it ran fine on my web server the first time I sent it up there.
As an aside, this week of evenings hacking on OpenID have been fun. This reminds me of a couple of years ago, when Dave Winer would propose something and an army of hackers from around the place would build it over the next few days/weeks. You don't get the chance that often to be part of an important piece of infrastructure like this.