Have you tried Azed or the Genius (both on guardian website) or prospect generalist (www.prospectmagazine.co.uk scroll down the rhs to download the xword)
All 3 are good xmas puzzles.
Good tip,roslyn---Generalist,I mean!And is there some special way of going about assigning them all to their right places,other than intelligent guesswork?This one's a bit more difficult than others of its kind I am familiar with.Do I need to be a trained mathematician or something?