Hello,
try this library I written:
http://laurent.le.goff.free.fr/blog/IMG/zip/sevenseg.zip
This version is suitable for common cathode and anode common, directly connected to the arduino, look at example, and the image in the zip file.
not exceed 6mA per LED (40mA max per pin)
I'll soon adapt this library for control by transistor, and no longer be limited current.