My secret weapon is a folding editor called Code Browser. http://tibleiz.net/code-browser/ -- with this, you can do a non-destructive (well, it only adds comments) folding of the source. This is a very fast way to get a better view of what's going on. I've used it many times when trying to make sense of legacy code.

That is, if you choose to go through with it. My real advice would be to avoid it altogether as many others here. It's going to be extremely frustrating no matter how you attack the problem.