I am hiding out in the US Desert Southwest with my new PRS505 and I need some help.

Could somone please explain to me about downloadable file types. I understand PDF and Sony BBoB (whatever that is), Those two are pretty automatic. What I need to know is: Can I download Mobipocket and/or MSReader files and/or software to use with my Sony Reader?
I love this little thing. We live out in the desert, about an hours drive to the nearest book store, in a very small house with minimal room for books, and I read all the time, so this was the perfect solution on all fronts. I have been web shopping since I bought it for some of the titles I want to read, but I really want to besure I download the right format, because I don't like reading on a computer screen. I print long e-mails so I can read them comfortably.

Can I download e-mail to the reader?
Thanks for your help in advance, and I look forward to "typing" with you all!