Came across this product while looking at PCWorld. Its a 802.11b or g (two versions) wireless card that connects directly to your XBox or PS2. Plus straight into the ethernet port on the card.
See it at http://www.linksys.com/splash/gameadapters_splash.asp
It's available at PCWorld for GBP79.99 (incl VAT), but its a pity that I don't have a wireless network at home to make use of it.
Still, I can just get a cross-over cable for less than GBP10 and be online :-)