Windows cheats in some respect - allowing you to login before it is really done.
For example - after loging in Windows, I have to wait before I can dial my PPPoE - and I have to wait before iTunes will start - etc.
Michael brings up a good point. On my WinXP Laptop, where I have a wireless 802.11G card, it doesn't pump the card until after the login. It doesn't attempt to mount network drives until after you login. A good portion of the startup is unique per user, it doesn't happen until after login.
Unix is going to mount its network drives, pump the network cards and such before you ever get the "login: " prompt. All the more reason you can't really compare to two operating systems.
Rob