Adding an ExtJS panel to an existing web application

While I've been writing C++, C# and Java for the past 10 years, web development is fairly new to me. As someone without a traditional web dev background, I've been asked to see 1) if ExtJS would allow me to be productive quicker on the web and 2) how easy it would be to integrate ExtJS into one of our existing web applications (currently built on the Symfony PHP-based MVC framework). The UI I'm working with is tab-based with the selected tab occupying the bottom 75% of the screen. What I'd like to do as a first step is to add a simple ExtJS panel to one of the existing tabs. I've read through several of the ExtJS docs and worked through a couple of simple example applications but I'm a little unclear on how to actually get ExtJS integrated into this existing application. Since I don't have the entire screen to work with, I'm assuming that I don't want a viewport as a root container but rather something like a panel? Thanks for any suggestions you might have!