http://ukbouldering.com/board/index.php/topic,1892.0.htmlthat should get you started
It's virtually impossible. Scrub that, it's impossible. Grades are so subjective and particularly so in bouldering where the tiniest difference in height / flexibilty / finger strengh / raw power etc can make one thing feel easy for one person and the living end for another. It's difficult enough getting people to agree 100% on the actual grade of most problems let alone getting agreement on what constitutes the benchmark at each grade. Sorry, this isn't helpful at all is it. It's just I can see how this thread might pan out! Good luck with it anyway.
Margaret? Margaret?!