Aquiring Network Address

Fed up with this message on my Belkin wireless network. Not alone
either, just set up a 'Wanadoo' wireless thing (big triangular box
transmitter thingy) and her laptop has the same message. (Desktop OK)

Now all would be OK if the scanning PC/Laptop actually DID aquire the
bloody network address .......... but it does not on both setups. On my
setup this message is only when I secure it with either WEP or WPA.
Software all up to date. The Wanadoo is also secure and the same
problem, it don't wanadoo it.

Any solutions in plain speak please .... can I allocate a network
address manually to each PC (how) and will it rid me of this wretched
message, and will I be able to secure my network.

TIA