Can i add 12v ps to Arduino Duemilenove?

Hello.

Can i add a 12v+ to my Arduino Duemilenove board?

Or what should i do?

If I got the right datasheet for duemillanove power suply chip click for pdf it should be ok, since it can take up to 20V. Just be carefull to connect it to the DC jack and not to a +5V pin or something (just saying...)