A: Make sure you've run the bbrb.inst script

A: The script is admittedly not too pretty good. I'm currently working on a version of bbrb that will do away with it completely. However, to get bbrb installed, you can run the bbrb.inst script like so:

$ bbrb.inst /path/to/your/blackbox/menu

It creates the directories ~/.blackbox ~/.blackbox/Styles and creates the files ~/.blackbox/Menu ~/.blackbox/bgMenu and modifies your .blackboxrc to point to the newly copied ~/.blackbox/Menu file. ~/.blackbox/Menu is a copy of the menu file you supplied to bbrb.inst and has an extra entry which includes the ~/.blackbox/bgMenu, where all your background entries will be stored.

If something messes up somewhere, delete these files and run the script again.

A: Make a symlink to your openbox/rc file like so:

$ ln -s ~/.openbox/rc ~/.blackboxrc

and then run the bbrb.inst script like so:

$ bbrb.inst /usr/share/openbox/menu #or whereever your menu file is.

A: Make a symlink to your fluxbox/init file like so:

$ ln -s ~/.fluxbox/init ~/.blackboxrc

and then run the bbrb.inst script like so:

$bbrb.inst /usr/share/fluxbox/menu #or wherever your menu file is.

Make sure the "session.screen0.rootCommand:" field in your ~/.fluxbox/init file is not set, since this will override the rootCommand: in the style file and bbrb will appear to do nothing. bbrb works by modifying a copy of your current style's rootCommand: entry.
Version 0.1.9 of fluxbox is known to work, earlier versions may not.