add 3 column display to WPG2

After messing with the css files for a little bit and searching the forum I wanted to know how hard it would be to add to the align section of the plugin.

Being that after I select the pictures from within wordpress (wpg2) and choose from:

Float left, Float right, centered ... etc

None of which really display nicely. Since I have the thumbnails set to 150px I would like to include another css align class to make a 3 column setup with say 5px between the photos... what files would i need to edit to add the layout to the drop down list?

Thanks,

Wonderliver.com