You have to rename the file "gp2xsound.wav", put it in the root of your soundcard, and hold down "start+select" when you boot.
HOWEVER!!!! I've read that the startup sound must be at a specific frequency and length (about 2 seconds?) to work. I'm not sure this sound would match those criterion...
Let me know what freq and ill make more. I am not a progammer by trade so as long as i have a framework to work on ill be happy to make more intros. Hardcore, drum and bass, electric guitar. You name it, ill give it a go.