Hi Erik
Imagemapster is a jQuery plugin and depends on jQuery to work - jQuery and Prototype can work together if you do it in the right order
first load jQuery then immediately run jQuery.noConflict() then load Prototype. jQuery uses the $() method by default - same as Prototype so the noconflict() method releases the $() method for Prototype.
So for the Imagemapster to work correctly - make sure you have jQuery loaded and then call it like this
jQuery('#usa').mapster({ // rest of options });
If this doesnt work then the Imagemapster javascript code depends on the $() method to be pointing to jQuery - all you need to to is replace the $() with jQuery() and then it should work
Let me know if you need anymore help