Personally I'd reconmend
LetsAutomate as they tend to be cheaper and the service is excellent.
To start with you need the switch, which as you say just replaces the standard rocker switch for the screen.
SW10G Wall Motor Drive Switch (£47)
This makes your screen X10 controllable.
Next you need some sort of X10 remote reciever.
IR7243 Infra-Red -> X10 Transmitter (£37.60)
(to use InfraRed)
or
TM13U X10 RF Receiver and X10 Transmitter (£19.95)
(to use RadioFreq)
This kind of depends on your current remote stack and if you want another for the pile. The RF receiver will need another remote like the KR19/22e keyfob types or if you have a UK Pronto remote with RF then that will work. Alternatively there are all in one remotes like the X10 EasyTouch Touchscreen Remote Control which could also replace your existing remotes if you haven't already got a learning remote.
If you have a favourite learning remote you like then the IR reciever might be easier as you can program your remote to control that (how depends on your remote).
X10 uses the mains wiring to transmit commands so once the switch is wired in to power you can plug a reciever into any socket in the house to control it (depending on your wiring you may need to use a local socket if you have seperate circuits/fuses).
Hope that helps. I'm not an expert, this is just what I learned from doing it myself as I didn't fancy my screen suppliers remote option as it was expensive, RF and I didn't fancy yet another remote on the sofa. When I asked them for a IR option they actually recommended looking at the X10 option which was kind a cool.
