Brian,
For the "_" and any other special characters, you need to press the ALT key (one next to the "Z") and then the shift (up arrow) key.
As far as the other questions on your list, check out
http://www.qusers.com/. I don't use mine for TV, MP3s, etc. but I have seen a lot of posts there about what you are asking. The registry hack to use the SD for email is there as well.