Windows 2003 Server with Exchange and Sharepoint Services 2.0

Hello,
I have a Windows 2003 server, which runs Exchange Server 2003. I installed
SharePoint Services 2.0 on Windows 2003 Server, which worked great.
Now, employees access their email from outside the company by using a static
IP address, but when I installed SharePoint Services 2.0 they were not able
to anymore. Why is that?
I tried to use another empty static IP address and put it into our router,
also using the private IP address of the Windows 2003 server, but I was
unable to do so; it wouldn't allow me to associate a private IP address with
2 public/static addresses.
Can I run SharePoint Services on Windows 2003 Server with Exchange Server?
Can users still access their email from outside the company?

Thanks!