Change default window icon

For windows that (I guess) don't have their own icons (Glade interface designer, mplayer, pygtk examples), an ugly big 'window icon' with blue bar appears in the dock. It irritates me, because:
- it's not my style
- it's enormous. almost 2-times the size of other icons
You can clearly see Glade's 4 windows in this screenshot of dock: http://shrani.si/?30/Cq/4z2rqYzV/uglyawn.jpg
Dock's size (bar height) is 32px.

Is there any possibility to change it to some other icon or resize it or something else? I've searched the awn gconf and awn folders and I haven't found anything. Do I have to change some icon in gnome icon set? I'm not even affraid to use python to make this less ugly.

This is on Ubuntu 7.10
Thanks alot