server 2003 & xp pro limited/admin user accounts

We have 3 offices which currently have 10 standalone desktops (each user can access their own PC from home via secure RealVNC) and 4 laptops. All have XP Pro, Office Pro 2003, AVG Anti-virus & Ad-Aware. There are 3 laser & 1 inkjet network printers. All are connected to Draytek Vigor2600v broadband routers. All users have been given Limited Accounts. Now we are expanding we have decided to have a Network Server installed with Windows Server Enterprise 2003, Exchange Server Enterprise 2003, Office Pro 2003 & AVG Anti-Virus. The dealer installing the Network has told us that each desktop user will have to be given Admin Accounts. I do not want to give them Administrator Accounts for obvious reasons. Why do we have to do this? On the current system before I moved all users to Limited Accounts I had nothing but trouble.