Vista - Can't connect to wireless router even though I know the password

I've not seen this problem before - would be grateful for help please.

I have just set up a newly installed standalone wireless laptop (Vista Home Premium sp1) - it's a Sony Vaio - but can't connect to the wireless ADSL modem Router. When I try to set up the connection, it finds the wireless SSID OK - I click on that and whereas I would normally expect to see a simple connect box so I could put in the 64bit WEP code, instead it shows a box which shows: username, password, domain (the latter may be greyed out).

I've setup Vista laptops many times before to simply connect to their wireless routers and it hasn't been a problem. This is a single standalone computer - no network was setup by me. To get round the problem for now, I have turned off the 64bit WEP security and left it unsecure.