Food for thought...

At what point does it simply become plagiarism?

The classic case would be George Harrison's 'My Sweet Lord', proved in court to be based upon the Chiffons' 'He's So Fine'... some lawyers made a fortune out of that... it's highly unlikely that George deliberately set out to 'parody' the song - had he used a 12 bar blues chord sequence, Chuck Berry (for example!) wouldn't have been able to sue him!!

Does admitting where you nicked the idea from really make it any different?