Without going into a long-winded dissertation, forget about using resistors. The differences in the "zero" point base (0 volts vs. 4 mA) and in how instrument designs handle voltages versus currents do not lend themselves to a simple conversion using only resistors.
A 0-5V/4-20mA signal conditioner can be bought for around $250. You will burn up that money in a heartbeat trying to configure and calibrate a homebrew resistor setup.
