Yea, I tried cutting away some parts of an NSF file with a hex editor as well, but it stopped working when I did it. I didn't continue the experiment thought, I just cut away a few bytes at the end.
Oh, Memblers you're right, I just downloaded the Dragon Warrior NSF and it is only 5 KB. I am currently using a 5 KB Tiger Heli NSF in my game that works fine, so it should be OK. I just got scared away because on zophars page it said that the DQ1 NSF file had 48 songs to it. Probably most "songs" are just a beep noise.