Bryan,
When I was doing relay circuit design, we used a rule of thumb that the coil current has to be 1.67 times the operate current. {We used current rather than voltage since the magnetic field is proportional to current, so the design tables we used specified the operate and release currents}
So I deduce that the operate current of your relay is about 3.2 mA. (48/9/1.67)
At 12 Volt, the current will be about 1.33 mA and therefore the relay won't operate.
What voltage does the parallel port provide?
Virtually any transistor can be used in this circuit. All you need to do is to ensure there is enough base current to saturate it. The rule of thumb is that the base current should be about 1/10 th of the collector current.