How can I do source level debugging? I know emacs and gdb are capable of it, but I can't for the life of me figure out how to get it going...

KDevelop

Check out one of the IDEs in the Sticky thread about them. If you're coming from Windows, your best bet is with Eclipse or Borland BuilderX since they don't use the autotools so you can easily setup your project. KDevelop is also easy to setup but harder than the other two.

Perhaps I wasn't clear.

How do I do source level debugging in emacs ?

(The main reason being that getting KDevelop or Anjuta to accept existing makefiles gracefully has frustrated me to no end.)