I went through this as well and consulted my DSL provider. What worked for me was to enter the WEP key (26 digit Alphanumeric code) instead of the requested "pass phrase".

Like all of you i too experienced wifi problems with vista, i bought a Dell D820 Latitude with an intel 3495 wireless card, Windows Vists 32bit Business plus a few more goodies. the wireless card always dropped the connection which showe to me there were some incompatibility issues going on, so i asked around and to my horror found I was not the only one and that the problem was not just with dell but all makes that had the same card . the issue has now been resolved by using the 4695agn intel card which was used with the Dell D830 to cure wireless drop. The root cause of the problem is that the Intel software is incompatible with Vista, however the drivers work but allow only Windows to control the wireless and not the Intel software as in Xp. So for all of you yes it is a software/driver issue which i beleive will be resolved when Vista SP1 appears unless individual wireless card manufacturers issue updates to work with vista.