Create out of office reply without Exchange

1. Create an auto-reply email template and save it as an Outlook template
2. Create a message reply to send an automatic reply to your emails
3. In Tools | Rules and Alerts create a new rule (Start from a blank rule, click Check messages when they arrive)
4. In Which condition(s) do you want to check? window select the Sent Only To Me
5. In What do you want to do with the message? window select the Reply using a specific template check box. In the Select A Reply Template dialog box, click the email template that you created as auto-reply template.

Edit: this rule will send the reply only one time to each sender (Outlook will save a list of email addresses it has responded to prevent sending repetitive replies, but if the Outlook is closed the list is deleted)

Use Tools -> Rules and Alerts to create a reply rule for received messages.

http://email.about.com/od/outlooktips/qt/et_auto_reply.htm

The above link will lead you to a step by step guide to setting up out of office replies on both Outlook 2003 and 2007.