Easiest way to move mail from Exchange 2003 to 2013

I am getting rid of my old server, which is Server 2003 SBE. We are using the Exchange on their, which is obviously 2003. We now have a new Server 2012 with Exchange 2013 on it. We are completely getting rid of the old server and just moving all the data to the new server. I only have 5 clients with email and do not want to mess around with migrating and upgrading versions of Exchange. What is my easiest way to get these five clients email from Exchange 2003 t0 2013? I went in and did an export on each client and exported to a .pst file, but when I looked at the size of the .pst file compared to the .ost file it is really small. Is a .pst file that much smaller than a .ost?? If I just export their .pst file and then import it once they are on the new server will this work??