I see that installed Exchange originally with CPG-ADMIN account and that's the same account you are using to Install SP2. That's fine.
a) Can you move Exchange SP3 from desktop to c:\exchsp3\
b) Disable BackupExec Remote service on Exchange Server.
Kill the service first and then disable it - while you upgrade SP3
c) Exchange 2007 SP2 - how to install.
follow the guide here.
http://msexchangeteam.com/archive/2009/08/28/452209.aspxthanks