accessing OWA internally

Split DNS.
You will need to create a new DNS zone on your server for mycompany.com
This will need to contain the internal IP address and host of mail.mycompany.com
If you have any services outside, such as a web site, then add the hosts to the DNS with the external IP address:

www type A IP 1.1.1.1
mail type A IP 192.168.1.1
ftp type A IP 1.1.1.2

etc

Simon.

waht kind of zone and should I name it, anything in particular.  Allow zone transfers to the whole forest or just domain?

It should be a primary, non AD integrated. The name should match your domain - domain.com or whatever. Transfers to other domain controllers only.
On the other domain controllers, set it as a secondary, non AD integrated. Same name, but point at your primary.

Simon.

I can't choose primary.  I already have a primary zone

oops, I mean I alrady have a primary zone with that name  mycompany.com and it will not let me create a new one.

Ok I just created two new zones and called them what I was looking for:

www.newcompany.com
mail.newcompany.com

added the internal IP to each zone and they both work.  Is this the correct method?  I don't want any DNS problems with the network, is why i am asking.

If you already have a zone called mycompany.com then you just need to add a host to that existing zone.
Type A, name mail with the internal IP address.
What you have done isn't correct and you should delete them.

A zone contains just a domain name - not hosts.

Thus: host.domain.tld
www.domain.com

Simon.

OK I added both the www and mail hosts to the primary zone with the private IPs and it works.
What was all the split DSN talk for?   Is this a split DNS?

thanks for your help :)