Out of Office auto-reply messages always add an "out of office" indicator to the subject of the message. If you would like to create an auto-reply for a reason other than being out of the office, you need to create a rule. 

To create an auto-reply rule in Outlook 2003 or 2007:
Note: the screen captures are from Outlook 2003,  but the windows are virtually the same in both versions.

1. From Outlook's Tools menu, select Rules and Alerts.
2. Click New Rule.
3. Select the Start from a blank rule option.
4. In the Step 1 box, select Check messages when they arrive.
   
   
   
5. Select the checkbox for where my name is in the To or CC box.
   Note: Messages sent to any listserv addresses that you subscribe to will not receive an auto-reply message since your name will not be in the To or CC field.
   
   
6. Click Next.
7. If you would like to add any exceptions, select them from this window and then click Next.
8. Select the have server reply using a specific message option.
   
   
9. In the Step 2 box in the same window, click the link a specific message.
   An email compose window opens.
10. Enter and format the text for the subject and the message you wish to use for your auto-reply.
    
    
     
11. Click Save and Close.
12. You will see that the link in Step 2 box now reflects the subject line you entered.
    Click Next.
    
    
    
13. In the Step 1 box, enter a name for your auto-reply rule.
    
    
14. If you want it to being working immediately, click Finish.
    If you want to toggle it on later, de-select: Turn on this rule and then click Finish.
    
15. Click Apply and then OK.