hey im not sure if this is the way to do it but its what ive been doin although it seems a bit weird.
i unzip into its (name of theme)_theme folder, then copy that folder into C:\Documents and Settings\(username)\.limewire\themes. then i copy one of the LWTP files in that folder (such as the other_theme.lwtp file) and paste it into the folder of the theme you downloaded. then i rename it to (name of theme)_theme.lwtp and cut and paste it back into the main themes folder. then in limewire go veiw, apply skins, refresh skins.

im sure theres another way but this is what ive found that worked when i couldnt find another way myself.