If you don't get the wizard, go to Mail, choose preferences, accounts, then press the plus symbol under the accounts pane.
Put in your name, e-mail address, and e-mail account password.
Then press continue.
Under account type, choose Exchange 2007. Your company must be running this version of Exchange. Not all companies do, so check with your friendly neighborhood systems administrator.
Give this account a name.
Then put in your mail server, again provided by whomever runs your Exchange server.
Make sure your username and password are entered correctly.
You can also choose to integrate your calendar and contacts.
Then choose SSL if your Exchange system supports it. One hopes it does, and press Continue again.
Check "Take Account online," review the summary to make sure it looks correct. Then Press Create.
It may take awhile the first time, but eventually, you should start to see your Exchange e-mail in the Mail app.