According to what I can find Exchange 2007 and 2010 both have 4gb minimum requirement plus a certain amount per mailbox. All our servers have 4gb. Will we be able to upgrade Exch 2003 to either 2007 or 2010 on our existing servers? We have about a dozen users.

Have you looked at these? Planning Memory Configurations (2007) http://technet.microsoft.com/en-us/library/bb738124(EXCHG.80).aspx Understanding Memory Configurations and Exchange Performance (2010) http://technet.microsoft.com/en-us/library/dd346700.aspx

Thanks. It looks like we'll be staying with Exchange 2003 as it does everything we need it to do for now.