"Your Mac must have an Intel Core 2 Duo, Core i3, Core i5, Core i7, or Xeon processor to run Lion. Find out if your current Mac has one of these processors by clicking the Apple icon at the top left of your screen, then choosing About This Mac."

pulled directly from apple.com

mere speculation on my part here, but I doubt it(Lion) will be much more processor intensive then the current release. Just a guess, but I seriously doubt they would release something that would bog down a core2 at this point...