How to configure OWA on SBS2003

I want to implement exchange OWA on SBS 2003. What do I need to do to configure SBS successfully. I have a straight forward set up, a router with a static IP and 10 users who are case workers. I have a SBS 2003 with active directory setup. Now my case workers need to have access to their email as well as the public calendar at all times. My question is what are the necessary steps to configure Exchange for OWA. We are a not for profit NGO, we can’t afford to pay for tech support. Thanks in advance for the help