FYI this has a Realtek RTL8188CUS chip.
To set up wifi for Raspbmc it is easy as Pi.
1. Install Raspbmc on your SD card. (See Tutorial)
2. In XBMC (once you have loaded it up keep the network cable inserted): Programs, Get More..., Network-Manager... Install
3. Set up Wifi in Network-Manager
4. Insert Dongle
5. (now the not so tricky bit) In either a SSH window or Command line (Accessed by the standby logo in the bottom left hand corner, first Exit then press the Esc key, then log in with: pi and password: raspberry) type:
sudo nano /etc/apt/sources.list
Then add the line under the current one:
deb [...] squeeze main non-free
Then press Ctrl and O
Then Ctrl X
sudo apt-get update
sudo apt-get install firmware-realtek
6. Then: sudo reboot
7. Network-Manager select and type in your network password.
8. Remove your network cable
Good Luck :D
This product works for the purpose I bought it for.