An error occurred. error code was 3221684229. Access is denied..

This seems to be a very common error when trying to install Exchange 2003 on a Windows 2008 server.   It has a very simple solution which requires you to run the setup file in a Vista Service Pack 2 environment.   This can easy be done by adjusting the properties of the setup.exe

Below are instructions on how to run Exchange Server 2007 in Microsoft Vista Service Pack 2 compatiblity mode:

Step 1:

Right click on setup.exe and then left click on properties

Step 2:

Click on the Compatiblity tab

Step 3:

Click the Run this program in compatibility mode for: 

Change to Windows Vista (Service Pack 2)  Then click apply and ok

You can now re run setup and it will work