If I understand it correctly: you have a RF switch and you would like to use that to open/close valves through OpenSprinkler, hence you need the receiver, is that right? You will need to know the encoding pattern of your RF switch. If it’s compatible with common RF power sockets, you can look at the Arduino RC-switch library (https://code.google.com/p/rc-switch/). In general you will have to reverse engineer and figure out the RF switch signals in order to decode it. I’ve written a series of blog posts in the past about reverse engineering wireless sensors:
http://rayshobby.net/reverse-engineer-wireless-temperature-humidity-rain-sensors-part-1/
the same methods can be used to reverse engineer other signals in general.