If you haven’t done so already, go check out (and hopefully use, afterwards) idproxy.net.
As written in idproxy.net’s about page:
idproxy.net acts as a bridge between these two worlds. You can sign in to idproxy.net using your Yahoo! account, and then create one or more OpenID accounts for use elsewhere on the Web.
Basically, if you have a Yahoo ID, you can sign-in and create an OpenID for yourself at idproxy.net thus allowing you to use your Yahoo ID and password to connect to any OpenID supported site.
Go try it out!