Configuration of internal DNS for Exchange Server 2003

I currently have a single internal DNS server, 2 Domain Controllers w/AD, and newly configured Exchange Server 2003.   I will be using my T1 providers public DNS for name resolution.  I called them up my T1 provider and they manually created a Zone file as per my request and directions.  Once that was completed, I went and changed my MX records to:

mail.domain (MX) 10 ns1.ispdomain.net
mail domain (MX) 10 ns2.ispdomain.net

My WAN interface of exchange i have my static address and the primary and seconard DNS setting is that of ns1 and ns1.  

FYI:  I left my exchange open, so i can eliminate any firewall anomolies.

Here is my IP scheme:
Exchange = 192.168.10.21
DNS1= 192.168.10.10
PDC= 192.168.10.12 (GC)
BDC= 192.168.10.13

My concern is that through out this entire setup, I am unconfortable with the settings within my internal DNS server.  I am also concerned with using my ISP's DNS server to resolve to my exchange, but this is how the setup is and will be.  Please enlighten me as to what settings are impartive to get my exchange server up and running.  I need to know anything I may be doing wrong, or perhaps steps i missed.

THank you in advance!