If you look up "sender" at Dabs you can find a Dabsvalue Video/Audio Sender 2.4Ghz for £30. It's far cheaper than other A/V Senders I could find so I crossed my fingers and ordered it.
It turns out to be the "Medion Wireless RF Transmission System". Even on the Medion website, the same product is listed for £50. The one I got from Dabs is the same product (product code MD 9048) but is styled differently. It's oval and silver compared to the black box on Medion's website.
It arrived this morning and was a snap to setup; just plug all the wires in and align the dishes between transmitter and receiver. No need to read the little paper manual. Only trick is that I needed to set the video resolution of my GF4 4400 to 800x600. For video, you also need to disable DirectX hardware acceleration (Display.Settings.Advanced.TroubleShoot). It easily beams the PC output through a wall to my TV and stereo about 10 meters away. It claims to have a range of 30 meters indoors and 100 meters outside.
This certainly isn't the highest quality method of playing digital media. The picture is reasonable although the colours have lost any subtlety. It's more like TV quality than DVD. The audio contains hiss. It's alright with the volume down at regular TV volume but it's noticeable when you crank it up. It's just like the bad old analogue days. I doubt other RF-based AV senders are any better.
So for £30, it's a cheap and dirty way to play your digital stuff in the living room. It will do until I finally splurge on a Media PC. For a complete solution, it's possible for the AV Sender to pass remote control IR signals back to the PC to control your media player of choice.