[Jared Russell]

First, since the 2010 rules have not yet been published, anything that anyone tells you regarding the legality of any component or methodology next year is pure speculation. That said, we can speculate that FIRST might choose to continue their policies from prior years into 2010 (there is a precedent of this...)

External co-processors have traditionally been allowed provided they meet all of the requirements for a "custom circuit". That is, they must be within a cost limit, be powered by the robot main battery, be protected by a 20A breaker, and must NOT directly control any outputs (motors, pneumatics, etc., since this would go around field control for enable/disable, etc.).