welcome to LQ. Your second question (which distro to use) is asked very often, look in the "Newbie" forum and you will see many threads on this topic. There will be no single right answer, so prepare to read a little bit. Any one of the major distros should be ok.
The first question is a bit harder to answer, especially if you don't know Linux yet. I think it would be a legimate goal to show differences between Windows and Linux and point to some of the advantages (maybe also disadvantages, like that support for new hardware is implemented later, because *official* drivers are not offered) of Linux.
To learn something about Linux I usually give advice to read the Rute Linux Tutorial (http://rute.2038bug.com/index.html.gz
) -- it's good, but it's as well command line centered. But there are informations on how to setup a web server etc. etc. that might help you for your presentation, too.