Open Outlook 2007 and go to Tools -> Account Settings.

Make sure you are on the E-mail tab and click "New."

Select "Microsoft Exchange, POP3, IMAP, or HTTP" and click Next.

On the following page, do not enter any information. Check "Manually configure server settings or additional server types" and click Next.

Select "Internet E-mail" and click Next.

Enter the following information.
Your Name: Enter your name as you want it to appear on outgoing messages.
E-mail Address: Your email address.
Account type: Select "IMAP."
Incoming mail server: imap.(your domain name)
Outgoing mail server (SMTP): smtp.(your domain name)
Click on "More Settings."

Click on the Outgoing Server tab.
Check "My outgoing server (SMTP) requires authentication."

Click on the Advanced tab. Where it says Outgoing server (SMTP): 25, change this to 2500.
Where it says "Root folder path" enter "INBOX" without quotes.

Click Okay, Next and then Finish.

Once this is complete, go back to Tools -> Account Settings -> Double click on your account -> Click on the More Settings button. Go to the Folders tab. Select the second radio button ("Choose an existing folder..."). Expand the tree and select your Sent Items folder.

Click Okay, Next and then Finish. Your setup is complete!