What components/files are in the theme?

Primarily, it's a similar process - ie extract all icons, get decompressed 3.71 RCO and put icons back in.  For PRXs, you'll need to find the new offsets.

With 3.71, there's an extra step though - apparently, for topmenu_icon.rco, you can only used decompressed images.  To do so, after you've customize your topmenu_icon.rco, download this, put in the same folder as RCO Editor.  After that, open your customized topmenu_icon.rco with the hacked version of RCO Editor, extract all icons, then replace all with it.

Hope that helps you! :)