I've just setup my Raspbmc to use wireless to reduce the cables needed to run it. I didnt find any easy guides to doing it online (probably because its so simple) so I thought I'd post one here.

I am using Raspbmc RC5 and an Edimax EW-7811UN. Its tiny, requires no additional software and runs with no extra power supply. Plus, its cheap, £10!

First, with a network cable plugged in, press the following:

Programs
Get More...
Network Manager
Install

You should see:
"Add-on Network Manager enabled"

Now go:

Programs
Network Manager
Add
Select you network
Type your password
OK

Now go back to the previous window with [Cancel]

Click [Status] to confirm you're connected.

Simple as that!