Just thought I would blow my own trumpet.
I have a USB wifi dongle, based on the zd1211 chipset/firmware.
And, I have plugged in to my Pi, and it connects to my wireless router OK, and gets a DHCP IP address. It took about an hour of messing about - but it works.
I have downloaded some flv files using get_iplayer to my Linux desktop PC, and now I have omxplayer running on the RaspberryPi playing one of those events through the USB wifi.
Pretty cool, as I could use this as part of a media centre rig, as there is no wired ethernet where my TV is located.