Signing a file, crypto checksum

From: Herbert (
Date: 02/19/04

Date: Thu, 19 Feb 2004 13:36:10 -0800

I need to create a crypto checksum (Hash) to dedect modifications to a file.
1. Where can I / should I store the hash value in the file(header)?
2. How can I access this location using .NET classes?

thank you, herbert