Microsoft, Exchange, 2003, New Setup

I have a client with 4 Hotels that we upgraded to sbs2003.  They also upgraded all hardware and changed the software for their booking software and POS software.  I sold them all the hardware and Have a Network support contract with them.  They have online realtime bookings that comes with the "all in one" hotel solution software.. it tracks phone calls... A third party hosts their emails and website and we setup the sbs Exchange pop3 connector.  We also had to setup up a ssl cert for the webres.. we upgraded 3 properties with success and obviously a few learning curves and stumbling blocks.  The forth property was postponed because the property was seasonal and then was sold.  The new owners brought in a new server already installed with Windows 2003 Enterprise server.  They then purchased Exchange 2007 but it would not install on the server because it was a 32 bit server and the new Exchange requires 64Bit.  So they reordered and purchased Exchange 2003.  I didn't install windows becasue they had "A Guy".  I just finished the updates when I got the server.  It took a while to get the Exchange 2003 software so the deadline is this week.  I installed exchange 2003 but got a warning that the version was not compatible.  I guess it was because it was exchange 2003 not 2003 enterprise.  But I ok'ed the warring and then Exchange installed.  I did the domain prep and forest prep and everything seemed to work.  The problem I am having is that this is not going to be setup to retrieve from a third party hoster for emails like the other three properties.  This new client wants to host their own post office.  I don't think the server domain is named the same as the email extension.  ex... domain is abcCom.local and email is client@cbaCa.com basically they are not the same.  I thought if you have an Exchange server and want to become a post office, that you have to name the domain the same as the email.  If not then could someone please send me a procedure to setup a new exchange server clients..there has got to be a procedure to follow that shows me what to do next and if the email can be different then how do I make the recipient policy and new email accounts first storage group.. etc..Is there filters or is it simple to setup Exchange.  This is my first one.  I know I have to change MX records but I want to make sure I have everything right.  Also ports in the router if possible.  Thank you in advance