I don't doubt Rambus has some IP, and some of it is probably great given that they have one of the best EE's, Mark Horowitz as one of the founders.
As far as which of it applies to RDRAM or SDRAM, I wouldn't know. It's fairly easy to patent anything in the world. I think whatever the invention was, Rambus seems like a giant lawfirm at this point, instead of coming out with new technologies to license they keep beating the dead horse about SDRAM.