First, from the Application Guidelines:
In addition, any portion of your MySpace Applications and MySpace Application Content [..] must not [...] contain or create SCRIPT tags pointing to external sources except those that are explicitly allowed;
Second, the MDP isn't an extension of iGoogle - it's a seperate and distinct platform.
As far as your PNG images, I'm not quite sure what your obfuscating, but you can always use a PHP script as the 'src' of any image you incorporate. Again, I'm not sure how helpful that would be to your situation, but I can't imagine why it wouldn't be.
And why does your MP3 player require an external PHP file? There are dozens of opensource and example SWF-based MP3 players that require nothing more than HTML to implement in your App. A search on any of the major Flash dev sites will find them for you.