asp.net and active directory

[LadyReader1]

I am using VS2003, coding a web app in vb.net. I need to check Active Directory to see if the user is a member of a particular department before enabling some buttons. I found some code that searches AD. It references namespace System.DirectoryServices but that is not an option on my system.

The error is:
"Type 'System.DirectoryServices.DirectoryEntry' is not defined".

How do I fix this?

Thank you.