Most of the sun4m workstation have a special connector for the keyboard. In this case the mouse is connected indifferently to left or the right side of the keyboard. Some computers have a PS2 connector, it is very easy to spot the difference. The keyboards you are the more likely to encounter are the type4 and type5.
At the time of this writting, I didn't manage to have mouse support on the Sun Blade 100. Things should become easier in the near future.