HELP! Need to retrieve Style directory list in dropdown box in acp

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Hello!
Just as the title implies, I need to be able to retrieve the Styles directory listing into a dropdown selection box in my addon options.

I am using this for the dropdown box in the options:

    <xen:selectunit label="{xen:phrase MY_ADDON}:" name="image_category" inputclass="autoSize" value="Default">
    </xen:selectunit>

How do I populate this code with my Styles Directory listing?
I have no idea what I am doing when it comes to listeners, helpers, handlers, etc...
so,
Any Help is much Appreciated... Thanks!