Exch 2000 with different local dns name

Dear Friends,
I need urgent help,
I have local domain name abc.com. But I have registered domain name abcd.com.
Now I want to load exchange server on my local server.Uptill now,users in my domain were connecting to some ISP exchnage server using POP account through wingate.But now I want ot set up exchange server.I want to keep local domain name as it is, but still want to use abcd.com for external email forwarding.Is it possible?what kind of dns settings are required to be done on the isp dns server?