http://support.microsoft.com/kb/311107
How to define a rule to send an automatic reply in Outlook 2003
1. On the Tools menu, click Rules and Alerts.
2. In the Rules and Alerts dialog box, click the New Rule button on the E-mail Rules tab.
3. In the Rules Wizard, click the Start from a blank rule button, click Check messages when they arrive, and then click Next.
4. Under Which condition(s) do you want to check?, click to select the Sent Only To Me check box or any other check box that you want, and then click Next.
5. Under What do you want to do with the message?, click to select the Reply using a specific template check box.
6. On the Step 2: Edit the Rule Description page of the wizard, click the underlined phrase a specific template.
7. In the Select A Reply Template dialog box, click the template that you saved in step 5 of the "How to Define an Automatic Reply Template" section, and then click Open.
8. Complete the Rules Wizard instructions, click Finish, and then click OK.
The Rules Wizard rule to "reply using a specific template" is designed to send the reply only one time to each sender during a session. This prevents Outlook from sending repetitive replies to a sender from whom you receive multiple messages.
During a session, Outlook remembers the list of users to whom it has responded. When you restart Outlook, this list is deleted and the rule is reset to start again for each sender.
NOTE: Outlook must be running for the Rules Wizard to automatically reply.
in #4 change the conditions to include a search on the subject or body for your specific word or phrase 
Filter and Automatic Resend? 
Linear Mode
