Their has been some source code, and a compiled .bin version of DCpaint, a Dreamcast painting program; made available. Here is what the author has to say:

Dream Paint

Move mouse wheel to change drawing colors.
Hold left button to draw.
Hold right button and move mouse to make a square.
Press both buttons (right & left) to erase the screen.
Side button returns to main screen.

Lots of bug, few features, code is messy.

Try to enjoy!