My recommendation? Either set up Google Apps for your domain (free), or if you really feel you want/need Exchange, then pay for a hosted exchange environment for your office. If you honestly want to host this internally, then hire a consultant to come in and help you out.
Granted, for what I'm guessing is a small environment (single server, under 100 users), Exchange isn't all that complicated to set up. From your question, though, I presume that you're coming into this with very little (if any) knowledge about Exchange. If that's the case, I can't honestly recommend setting it up yourself. Running a mail system is not a fun job, and to do it in a stable/secure manner requires quite a bit of work, understanding, and time.
As an example, look at all the Colleges and Universities that are outsourcing mail service for their students and staff to either Google (Google Apps for Education) or Microsoft (live@edu). Those universities certainly have the knowledge on staff to run an effective mail service for tens of thousands of students, but are still choosing to outsource - partly due to the money savings that come along with outsourcing email, but also partly due to the desire to get rid of the annoyance of maintaining an email system.