Okay, it turns out the guy who made the mpguino didn't use a bootloader, so I guess I don't need to worry about that.
All i have is the .cpp file. I just ordered a duemilanove. So as I understand it (correct me if i'm wrong) I just need to download the arduino IDE software, plug in the duemilanove and install the driver file, then i should be able to load the .cpp code into a new sketch, and then upload that to the chip right?