use .xsession file
in your home dir create .xsession
it is shell script vulgaris: you put whatever you want to happen when X server runs.
This one will start xterm and blackbox every time you log in.
You MUST call window manager LAST. Also, be careful to run all other programs (except window manager) in background, becouse it will hang the server.
When you're happy with the script, save it and make it executable.
Every time you log in, instead of looking in default xsession, server will look in your ~/.xsession file.