3 field Logon - looking for guidance!

[Bill]

I have an existing app using homegrown code for login authentication and am
in the process of updating the site to net 2.0

I would really like to use the Login controls and Membership provider but I
have a 3 field login

Company
User
Password

I don't want to give up on this unless I have to, since we may have multiple
"john Smiths" from different companies

Could I stitch the user, password ASP membership model and my company name
together to make a 3 field login?
perhaps by appending the companyname to the username before submitting for
validation?

How about a 3 field custom provider - would this be hard? Any examples out
there?

I read the recent post about multiple Membership.ApplicationName and I don't
really see that as a solution sincce I am dealing with hundreds of
companies.


Any comments or suggestions would be much appreciated

Thanks

Bill