Domain Name Structure

hey
you can use the same name for you internet and internal network
i would assume you have already registered your internet name
the only drawback to using the same namespace for external and internal networks is that it opens up the possibilityof unauthorized people getting access to your internal network
if you really want to use the same namespace i would recommend using 2 dns servers. delegate one dns server with a zone for your external network (anything that you want to be seen on the net), make sure this is a secondary dns zone too (so the zone file is read only), and then configure another dns server for your internal network, and include the ip address of the external dns in the forwarders to allow access to the net from youinternal network

I think the best way is to use different names, for example you bought the newbusiness.com it is wise to use newbusiness.local to differentiate between internal and external networks.
I've forgotten a whole lot of reasons but when you search on microsoft.com there should be a document about designing a dns structure for your network.