I've done some searching, and see no easy way to tell who is or had accessed my wireless network.
For example, I was in an apartment once in Europe and found a wireless network in the building. I tried to get on, but of course, it was password protected (WEP ?).
Is there any way for me to tell if my neighbors are attempting to sign in on my WEP encrypted network? Can you tell if they successfully guess your password and log in?