Exchange server setup

Hello all,

Im trying to setup an exchange server at our shop.I have a dot.com
site well just call mysite.com. That sight is hosted by veritas. I went in and pointed my mx record to my instagate internet appliance(24.24.x.x).from that appliance i point it to my NEW exchange server(192.168.5.11).in my pc i type 192.168.5.11 in my outlook servers.Now i think my problem lyes in the domain name. the instage box is mysite.com and the server is notmysite.com. does this matter ? will I have to reload the server to change the name since it is the domain controller. I have no problem doing this if that what it takes. I know that veritas is forwarding propery cause if i leave the exchange out of the mix and go directly to the instagate i recieve my mail. So i guess i need to know the following...
1) does instagate and exchange server have to be in the same domain and if not is it easier if i make that change?

2) does the exchange server need its own EXTERNAL ip address just for that?

3) what domain does pc have to be a member of.

4) is just putting in INTERNAL ip of exchange server into outlook servers the proper way.?

So here is the current senerio


1) mysite.com (externally hosted) 24.25.26.27

2) mysite.com (internal instagate box) ext 24.x.x.x  int 192.168.5.3

3) exchange server (notmysite.com)(windows 2000 server)192.168.5.11

4) dhcp assigned by instagate to workstations

I have tried setting up exchange server 2 previous  times now in the last year.
Obviously no luck (or Time)
Please dont let me strike out....
 
If there are things I`m missing please feel free to include them.


Thank You in advance   Tim Hemmerich