Hi Mike,
You can use the Provider Model, specifically the Membership Provider Model,
with the System.Web.Security.ActiveDirectoryMembershipProvider class. Here
are a few references:
http://msdn2.microsoft.com/en-us/library/aa479030.aspx
http://msdn2.microsoft.com/en-us/library/aa479031.aspx
http://msdn2.microsoft.com/en-us/library/aa479032.aspx

Signature
HTH,
Kevin Spencer
Microsoft MVP
Printing Components, Email Components,
FTP Client Classes, Enhanced Data Controls, much more.
DSI PrintManager, Miradyne Component Libraries:
http://www.miradyne.net
>I am currently authenticating my users based upon a check to see if
> their details exist in a database table. How do you authenticate users
> based upon their Windows login?
>
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