Midi Library - Different Serial Port

Hi Everyone, First time user to the board. I am having an issue using the Midi Library on the default serial port (0). I am using the USB connected to the computer as well so my thought is the two are conflicting. Therefore I am trying to figure out how to point the Library to a different serial port. I am using the Arduino Duemilanove. Can someone please point me in the right direction? Thanks in advance!