By default, Plananarama will run in remapping mode. Remapping mode is the most convenient of Plananarama's display modes because it allows you to simply make any Hollywood script run on all kinds of palette screens. You don't have to adapt your code in any way, it will just work because all graphics are remapped to match the target screen's palette. However, this means lots of work for the CPU so it will be very slow. Also, it means that all images will be stored as RGB graphics which will consume a lot of memory. For example, a 640x480 image will require 1.2 megabytes of memory when stored as RGB but only 300kb of memory when stored as a palette image.
To speed things up, you could try using palette mode instead but this will require you to tailor your script specifically to the constraints of a palette-based display. See Palette mode for details.
Note that when using Plananarama in remapping mode, it's advised to install FBlit. See Requirements for details.