My company is moving from Novell/IPX to NT 4.0 and TCP/IP with DHCP. I've always worked with IPX but never TCP/IP so I need help in clarifying some questions.

Our company has a domain name registered and been given an IP address. This is for the web site that is hosted on an local ISP. When configuring my internal NT server to use TCP/IP and DHCP:
1. Can I use this same IP address for the internal NT server?
2. If so, what valid IP ranges can I use for the DHCP?
3. If not, do I need to obtain a new domain name/IP address for our internal network if we plan on connecting this server to the Internet?

I also need to connect to my ISP to download our whole company's e-mail. I've heard that to do this with Exchange Server 5.5, I need to obtain a fixed IP address from my ISP.

I know all this might sound confusing (because I AM confused) and even trivial but I don't know where to start.

TIA
John.