http://sudoku.com.au/ - the ones I do
http://sudoku.com./ - the rules (click on the left hand side)
I read about the craze a while ago. I started out yesterday on the one our local paper prints up. I worked on it from 1:30 to 7:30, (heh, also watching a tennis match) and finished it! In the interest of full disclosure, I should also say that we found the site that "helps you out" if you need it. I needed it - in the form of 3 filled boxes, a filled-in column and Madre and the Bro helping out in the end
(The one above is not that difficulty level, by any stretch).
Note the check mark next to "easy" on the ones I do! The Bro is more naturally talented at Sudoku, which stands to reason - computer guru, guy, blah blah blah.