Spearfish

I have a small 12 user dental office that wants to implement SBS2003 so that they can utilize the calander sharing feature, but they also want exchange to handle the email for the company. Whats the best way to do this? Iknow about POP3 connectors, but they want the exchange server to be the POP server. and represent there domain on the internet. Can I host the domain on my data center server, then somehow point mail for that domin to the local exchange server that has a dynamic IP? JS