My suggestion is similar to Nick's. Once you understand the pieces he mentioned then you can start using some of the tools.
There is quite a bit on YouTube and TheAcademyPro.com, but you have to know what you are looking for. I would suggesting downloading BackTrack3 (or 4 Beta) and going through each of the installed tools. For each tool, do a search on YouTube and see what comes up. You might be able to follow some rabbit trails to find other things that interest you.
BT includes MetaSploit, and researching that one will be a significant project. It is a very powerful tool and there are lots of pieces and options for that one.