"Patented" is the wrong word here. It would be either copyright or trademark, and the system is definitely copyrighted; I don't know whether it's been trademarked as well. Using R&K (in modified form or otherwise) would definitely constitute a derivative work under copyright law, and the odds of it counting as fair use are pretty low. Unless R&K was included in the sale, we'll be looking at a new system.
(My previous message got buried in the earlier part of the thread because it had to wait for mod approval, so: <waves hi to everyone>)
Hey!
I thought "dice systems" were a grey area in the law -- or did we end up with everyone and their brother using d20 derivatives because of aftereffects of the "open gaming license" ?
I'm prety sure that mechanical bits and pieces like "percentile dice", "roll under" / "roll over", target numbers, dice pools, and such, aren't really considered protected IP.
Has there ever been a court case involving RPG mechanics?