Voltage level shifter
Check out Sparkfun's Logic Level converter. It includes a schematic, you should be able to do almost exactly the same thing by hand, but you'll probably need to use different resistor values to get the correct voltages. It includes two circuits, one for connecting a low voltage transmitter to a high voltage receiver, and one for connecting a high voltage transmitter to a low voltage receiver. It sounds like the former is what you're asking for.