My installation of Mandrake 10 didnt include Blackbox, but i guess i forgot to check it durnig the installation bit.
You can either download the latest Blackbox WM from their site (cant remember it now, blackboxwm.sourceforge.net i think it is)
Or, go to the command line and type:
with a bit of luck that should list the packages, which you can then install. Use rpmdrake and install it straight from your CDs
Another option is to have a look at something called Fluxbox, which is very similar to Blackbox in how it functions. Its your call