PHP best practices

I'm currently working for a company that uses the LAMP application stack. They have only had one full time programmer since they started, and he's a cowboy. They don't use much of a database abstraction layer, they mix their display code with their business logic, they don't do any testing, and even worse than not using source control at all, they sometimes use source control.

I'm starting a new project that will be fairly large and independent from the rest of the site, so I'd like to introduce some better development practices. I don't know much about php frameworks and stuff, so if you have any suggestions for what I should use please post them in the comments. The only major requirement is that it can be used along side the existing code. So what do you suggest?

Comments

Anonymous: cake? ask luca about webhp

Cezar: Yea, I've heard cake is good. Make sure you get an ORM. That's pretty much essential. Try getting them to let you use mercurial. And honestly. If they are high traffic and have no tests, then that's a huge mess.

Luca: I used CodeIgnitor and thought was pretty cool.