Knusperkeks, that answer depends on the key. You'll forgive me, please don't take this personally, but I am always vaguely suspicious of people whose first question on these boards relates to the pentesting capabilities of these devices.

May I ask - for what purpose do you want to perform WEP password cracking? If it is simply because you have forgotten your key, then there may be better alternatives available; returning your wireless router to factory defaults and re-configuring is usually a much easier route than trying to crack the key, especially if there is little traffic.