Actually, what you want to use is the Out Of Office Assistant. Here's what to do:
In Outlook, go to TOOLS - OUT OF OFFICE ASSISTANT
Click on the "I am currently out of the office" button and make sure the text box under that is EMPTY! If you don't your customers will receive 2 auto replies.
Click the "Add Rule" button.
Now click the "Reply with" check box near the bottom and click the "Template" button.
When you click the template button, a new window opens up that looks like a new message window.
Leave all the fields blank except for the Subject and body of your auto reply. In the body of this template, create the auto reply as you want it displayed to those who send you the email.
Now in the template you just created, click FILE - SAVE & CLOSE. This will save your template as your auto-reply.
Click "OK" on the "Edit Rule" window. You'll see a window asking you if you want this rule to fire for all incoming messages. Click YES! Click OK again on the "Out of Office Assistant" window and you're all set.
Every time they open Outlook it will ask if they want to turn off their out-of-office. Click no to keep the auto-reply in place.
Hope this helps.