Can't give you a cookbook on using Symfony2 forms independently. You can keep an eye on the S2 forums. Couple of people seem to be working on it. Rendering the actual html output is done within the framework. That might be the most difficult part to figure out. Of course you can always consider wrapping your framework inside of Symfony2. I did that to my own framework.
PEAR Forms is not really obsolete. Might give it another look.