it could be the plus setup comparing your 98 serial key against the cd key, maybe it won't install if they don't match.
you don't really need the setup to extract the saver though, in the plus folder..you should see a compressed cab 'plus98' this contains all the screensavers and other files
just extract the scr files from it, the wild animals should be there
i did the same with my plus98 but not sure if there is an animals saver..i couldn't check them all and just uploaded all the plus savers there, check that 7zip if t has that screensaver you want
http://kmext.sf.net/libraries/98plusscr.7z