Arduino with x10 power line? Arduino with RS232?

After realizing that we had a c290 controller module, I have decided to mess with that.

It has a 5 pin connection on the back (old style large DIN), 3 of which allow serial communication (input/output and ground).

Now, it uses a special style of communication apparently, and me being more of a novice, haven't gotten around that point yet.

If anyone else wants to help take a crack at this or share some knowledge, I would appreciate it very very much.

here is the manual with the information:
http://www.smarthome.com/manuals/MAN-1130_31p.pdf

Thanks!

Ben