Will it work with Photoshop 5.5 on a Mac?
The problem is not with Photoshop and Mac since you can install Windows through Bootcamp or Parallels Desktop. The problem is with KPT and Photoshop since their compatibility is highly questionable. I've found a discussion post on the Photoshop boards where this matter is discussed. Access it through the link posted below, but I doubt the KPT will work anymore since it's way outdated.
Here is the link with the discussion: https://feedback.photoshop.com/photoshop_family/topics/what_is_with_the_installation_of_kpt_filters_in_photoshop_cs5