This might be an acceptable and cheaper wireless solution for some, but (a) It's not tested, and (b) It's not 802.11b, but it is cheap.
Netgear sells a wireless multimedia system that uses the Whitecap technology - it's 11mbps but not 802.11b. Supposedly it is better for multimedia applications that require a constant bandwidth, and is being used in the forthcoming 802.11e standard. Some background info here:
http://www.sharewave.com/Products/WhiteCap/whitecap.html
Anyway, the kit consists of a PCI card and an ethernet bridge. The original price (e.g. on Amazon) was $300 but the Netgear store is selling them for $70 (or individually for $40 and $30 for the bridge, and PCI card respectively).
http://www.netgear.com/product_view.asp?xrp=11&yrp=31&zrp=103
Netgear also seems to be selling them directly on eBay e.g.
http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1325765821
I emailed Netgear techsupport to ask if there was any way to just have two bridges (i.e. on on the Rio and one on a router) and they said no, but they say it should be fine with the PCI card in your PC and the bridge on the Rio. I should point out that I haven't done this myself, so if it doesn't work, please don't come crying to me (and also, if you have reason to believe that it wouldn't work well with the Rio Receiver, please say something).
The manuals are available on the Netgear site as downloadable .pdf's.
Not sure about availability in the UK - the UK Netgear site seems to link to the US store.
Of course, what would be really cool would be an adapter between either the ethernet or HomePNA port and the new Homeplug mains-based system, which seems more elegant than wireless for anything besides truly mobile devices.
Hope this is of use to someone.
- Gary