Hrmph -- I thought they worked on macs too.

The other thing you can do is search your computer for a file "default_osx_theme.lwtp". Make sure you copy the theme files you download (via the HTTP link this time) to that folder. Then, if LimeWire is already running, choose View -> Apply Themes -> Refresh Theme, and then View -> Apply Themes -> <your new theme>. Or, in place of choosing the refresh option, you can just restart LimeWire.

Hope that helps.