"Does Presenter allow for the insertion of multiple mp3 files
per slide"
No. Presenter is a single audio thread tool. You can add
additional audio through a SWF or FLV file on the slide, but that
is the only work around.
"and to be in sync with custom animation?"
Yes, you can sync animations with the audio of the slide. But
understand that syncing it with SWF's or FLV's is a challenge that
is not worth undertaking for most. I have seen some... creative
solutions posted here for that, but most of us are best off just
letting that path go.
Jorma@RealEyes