In addition to open source physics engines and books, online resources are also a great place to research game physics. There are several blogs and publications available. I highly recommend publications from valve:
In addition to the mentioned blogs, there are several videos and presentations on various physics topics available on the GDC vault:
There is also a list of relevant GDC presentations hosted on the Box2D website at http://box2d.org/files.
Of course, everyone runs into issues writing code, and physics is an especially difficult topic. If you run into issues with your physics engine, you can always ask for help at the following Gamedev.net forum: