another (more interactive) option might be to pickup a standard compilers text-book e.g aho-ullman / aho-ullman-sethi and follow the intro-compilers course-work available at any of the universities (e.g. stanford). work through the exercises i.e. hack, hack, hack !

at least at stanford, you will end up writing a small compiler for a toy java like language. kind of nice. from there you can go onto more mature stuff e.g. llvm.

edit: it would be even more fun, if you could take the tests too (within stipulated times ofcourse).