Today I spend some time writing Cocoa plugin classes for the tabpanel. You can soon use this classes to control more of the properties the tabpanel controls in REALbasic. Be aware that this is Mac OS X only for the Cocoa target:
So you can have the tabs on all sides, have small or mini tabs, use transparency and even hide all tabs or use a simple line border.
For now you can't change the colors of the tabs except for gray as Apple uses images for this and not a color property.