hardware requirements for a 1.1 asp.net application

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I'm tring to define hardware requirements for my
1.1 asp.net application. The app is a common
three tier architeture, nothing sophisticated.
This is composed by a DB classe that create/open
database connections and execute queries returning
datareaders results to Business Object
Layer that is accessed inside a Interface Layer
(private void Page_Load).

The application has an average of 2000 users simultaneous.

I would like hardware requirements/configurations suggestions
and also for documentation that help me to figure out it.

thanks