Ok I figured it out
This:
{$config.BASE_URL}/images/{$style_array.general}/newpm.gif
equals this:
http://www.yourdomain.com/forums/images/general/default/newpm.gif
Now this is assuming your style is the default board style. If you are using a style with it's own image folder such as "beagleworld" then "default" would be "beagleworld".