I really advice you to go RS485. RS485 is easy to interface, it is just like RS232...... usees the things with the diference that the voltage in the Transmiting lines is diferencial. As a diferemce from RS232..... you can "daisy chain" a whole bunch (I believe upto 16) different devices, you must use a "protocol" to address each one, and have a master that control the whole thing.
[DEVICE 1]<-----+-------->[MASTER]
[DEVICE 2]<-----|
[DEVICE 2]<-----|
You can use a rs232 to rs485 converter in case your master or devices uses RS232. Or a RS485-TTL converter in case you are using something like a microcontroller.
This will be of your interest **broken link removed**
I hope it helps some
Ivancho