This is when I really wish I had a scanner...

Robin Hood ha Jowan Vyghan
An dheu res eth dhe n fer O
Ha ny wra mos dhe n gellywyk wer
Pyth wrellons ena dhe vyras O

Sorry, but I'm giving up on this. If you have a really good reason for knowing this in Cornish by tomorrow I'll help. Otherwise buy the book that I mentioned above. It gives pronounciation advice too.

The book gives a bit about the history, basically concluding that no-one knows the origin. There's a reference as early as 1660 to 'Haile an Taw'

Sorry for not helping more, but typing Cornish for a stranger on a Friday night, well I have to draw the line somewhere...

Ed