Advice for using music written for other instruments:
Don't forget that a whistle is a transposing instrument - don't bust a gut trying to play a fiddle tune in A on an Eb whistle, just pretend that the whistle is an A whistle. Also, if the tune doesn't work because it goes out of the range of the whistle, try pretending the whistle is a fifth below (eg. if the music is in A, pretend that the whistle is a D).