Besides changing the top side drivers to PNP (like shown in my diagram and commented to by Erik) get rid of the extra resistor on the common leg of the display. In my diagram I showed a common anaode configuration and there should NOT be a resistor in the common anode leg. The reason for this is because as the display runs there will be a variable number of segments lit. This extra resistor will drop voltage proportional to the number of lit segments and cause the segments to dim when more become lit.

My circuit diagram can be easily reconfigured for a common cathode type design by adding more PNP transistors at the top side to drive "segments" and correspondingly lowering the number of NPNs that would now be driving the common cathode connections. For the common cathode type display move the series resistors into the collector circuits of the PNP "segment" drivers.

Michael Karas