I have one employee leaving and a new employee joining. Can I just rename the user account of the old employee with the name of the the new employee? Can I do the same for the exchange account? I am using Windows SBS 2008.
I never used small business server (SBS), but since it is basically an all in one AD based environment:
1) Yes, you can rename a user name. The name however is not how windows identifies an account. It used an unique identifier for that (e.g. s-12345-67890-12345-12345-12345). The name is merely the human friendly translation of that number.
This means that as far windows/Active directory is concerned both the new name and the old name are the same person. They have the same rights etc. This might be precisely what you want. Might. Since the old user is the same as the new user he or she also gets access to all* files that the old user had access to.
2) Why rename the exchange account? I would have thought that two email addresses would serve you better. A new account for the new employee. And the old account setup so that it either returns the mail for the person who left to sender, or returns a mail with "Person A has left this company. Person B with this mail address is his replacement. Please use that address in the future.".