Stan, thank you for the explanation about using diodes to drop the voltage. In the spirit of discussion, even though Dusty asked about using one resistor to drop the voltage, maybe he was thinking of a voltage divider circuit.
My understanding of the voltage divider is that, the tapped voltage (in between two series resistors) stays consistent regardless of current flow. Even though there's a little more to it, the math to determine the tapped voltage, as I understand it, basically boils down to making the resistor values proportional to the ratios of voltages dropped across each of the 2 resistors. Granted the resistors would need to have a high enough wattage rating to supply the current required by what ever load is being fed by them (plus the total load the resistors impose). They would likely produce a fair amount of heat (depending on the load) and perhaps not work as efficiently as using diodes. So in essence, probably not as practical as using discrete diodes or bridge rectifiers.
Link to Voltage Dividers Explained
