Usually once a successful connection is made the key is stored and
doesn't need to be input again. Are you getting a wireless connection
established ( i.e. able to browse internet / e-mail ) ?

Yes I get connected ok but my WEP key isn't being stored and I have
to keep reentering it! NB I Have another PC with Linux Mint 11 running on it
and exactly the same thing is happening.

Try manually creating the connection using 'Edit Connections' and make
sure that the 'Apply to all users' box is ticked.

Thanks,I have done that and the problem has been resolved.

As an aside, WEP has proven to be insecure. If your router supports it, WPA is a
much better choice.

yes appreciate that but unable to connect with WPA even with help from
ISP!

Both sides of the link need to be compatible so perhaps the Wi-Fi card
in this Ubuntu system doesn't have WPA or doesn't do it as the router
is expecting. Seen that sort of thing myself when an adapter that
*should* have been WPA compatible don't get on with WPA routers !!
Only way around it is to use a different Wi-Fi adapter or different
Router.

FWIW - if you are in a remote location then WEP is probably enough but
in a suburban or city environment it really is 'open house' for anyone
so you'd need other security options like MAC address filtering or
even severely restricting the DHCP range of addresses - if you only
allow one address then when you are connected the DHCP server will not
be allowed to provide another address for anyone trying to piggy-back
your Wi-Fi

and if you dont secure the router admin passwords there is no point, getting
in is still easy, just slows down the lessor experienced!