My friends have given me a song they want me to learn, its in mp3 format. They originally recorded it in D, but now they want to play it in C. How can I import this song into HomeStudio 6 and shift the entire pitch one whole step down but keep the tempo the same? Can it be done?

Most editing software can do this, some will really trash the song but still good enough to play along with. I use Wave lab which works fine if you tell it to do the slow rendering. You can try using the free version of Audacity, and there is a demo of this DJ software that does a good job too. Virtual DJ. 

http://www.virtualdj.com/

Not sure if HS does any pitch changes but if it does it will be on your process list.