PHP or RoR?

The Agile book says that you should start with the appendices if you have yet to use Ruby. In there, you get the basics on all the syntax. If you are just blindly going through the motions and copying the books code without understanding, how can you learn?

That said, unless you are familiar with web development, go with PHP first. I think its a very good thing to learn the nuts and bolts of whats going on in your application before moving onto a framework, something that abstracts away a lot of those nuts and bolts. If you don't understand whats going on underneath it all, you will never really understand how things are working on the surface.

Good luck!