On the V-to (4-20mA) conversion you can find several solutions based on XTR.. IC ( **broken link removed**) or you can use standard current source, such as for example LM304, and build a circuit based on that IC.
At the other end, you don't need anything fancy, just 250Ω termination resistor, and that gives you 1V-5V conversion, and any standard 0-5V A/D converter will do the rest.
Regards,
IanP