Hi...!

The GPO is an open-collector output, therefore it's easier to
use a PNP transistor insted of a NPN. check this circuit:

http://w1.380.telia.com/~u38009707/pnp.JPG

this uses PNP transistors to offload the GPO interface, the
first one doesn't need to be a big one.. a cheap BC556 will
do ...