Hello everyone and thanks for your help in advance.  I am upgrading from Exchange 2003 to Exchange 2013 and need to transfer approximately 40 mailboxes.  Each user has local OST files on their client machines.  I know there is no direct upgrade from 2003 to 2013 and would prefer to do a new install rather than upgrading to 2010 then to 2013.  I know I can use a third party converter to convert the OST to PST, then import them to Exchange.  But I was wondering what would happen if I performed the new install, then set up the new mailboxes for each user on the new Exchange box, then connect the users.  Will the local OST files populate the Exchange mailboxes?  Or will Exchange overwrite the local OST files with blank data?  Or will nothing happen.  Any insight would be greatly appreciated.

Seriously, stand up an Exchange 2010 server and migrate to it first.  By doing this cheaply you're likely to end up with a system that's going to be unsuitable in several ways.