In case anyone is still wondering, I put " multiwii_2_1_mega2_0_gps" (note spelling) into google, downloaded the ZIP from the first result, copied it into my library folder, opened the IDE, opened the example, set "board" to a "Nano 328", and compiled it.
Here's the error message I got:
Binary sketch size: 30280 bytes (of a 30720 byte maximum)
Edit: I should point out that I don't know if it would actually run on a Nano, but it does most definitely compile straight out of the box.
It is amazing how much time and effort moderators put in helping people out.
I would like to thank the moderators for their effort; even in hopeless cases.
Thank you very mutch