gaim uses GTK2.0+ themes. afaik i have never heard about any skins for gaim, neither have gaim ever said that it is skinnable.
if you are using gnome then gaim will take up the look that gnome is using while in KDE it will just take window borders of effective KDE theme. if anyone knows about any gaim skins it will be really nice thing for me too.
sorry can't be of any more help