Not seen that...
If your router allows, you may be able to allocate a "fixed" IP address, based on the MAC number. My router allows that, which gives that warm feeling of security - and takes all the pain out of setting up the connection when you turn on the laptop.
Anything not on the list of allocated IP addresses by MAC number gets thrown off. Stops the kid next door "borrowing" my Internet connection!
I use 64-bit WEP, but that's a 12-digit hex number (sometimes it needs dashes between each pair, sometimes not).