If you really have to go wireless (seriously, I wouldn't recommend it for a desktop) then an internal PCI wireless card will be more reliable than a USB one. there are currently 3 main levels of wireless, in order they are
802.11b (11mps maximum speed)
802.11g (54mps maximum speed)
802.11n (300mps maximum speed)
The orange livebox is a 802.11g device so the maximum speed you'll get on the wireless to it is 54mps (which gives a real world transfer rate of about 20-24mps). if you do buy a 802.11n card the card will drop back down to 802.11g when connected to the livebox.
But I stand by my first response, buy a long cable, tack it neatly round the room, a cabled connection to the livbox will give you 100mbs all day everyday... with wireless you'll be running about a 1/4 of that speed if only one computer is using the wireless, if you have two computers using the wireless the speed is shared between them so you'll only get about 10mbs.