There are some PrE Effects, that are only available on the PC, though not for the Mac, but I do not have a list handy,
I do not recall if Green Screen Keying might be one of them.
Perhaps our MOD, Steve Grisettin, who is fully X-platform, can comment.
As I show you in my books, the Mac version of Premiere Elements does not include effects for Chroma Key, Greenscreen or Bluescreen Key. As an alternative, you should use Videomerge.
Thanks Bill. Yeah, I think I saw that Green Key is on the PC version, but not Mac.
Thanks Steve, I will check out your book andlook into videomerge. I appreciate the reply.