Hi Kent,
On a local network intranet you can use Windows Authentication (assuming all the client computers are part of an Active Directory Domain and the web server is also part of the domain) and then users never have to login (or register) because it uses their windows login, but this cannot work over the internet and can only work with IE (or with a plugin for Firefox).
On the internet it is not possible to use Windows authentication though you can use Active Directory via Forms Authentication, but there is no way to have automatic login in this scenario.
Hope it helps,
Joe