You can do it in Outlook using the rules wizard.

First, create a new template that will say what you want to say in the reply. Start a new message, type "I will be out of the office...." into the message body, select File, Save As, change the file type to Outlook Template, and give it a name and save. Cancel the message.

From the main Outlook menu do the following

Tools
Rules Wizard
New
Check Messages When They Arrive - Next
Don't check any boxes - Next (you get question about applying to all msgs - click OK)
Check "Reply using a specific template.
Click the underlined "Specific Template" in the lower pane.
Change "Look in" to User Templates and select the one you just created.
Add any exceptions and finish.

This will require Outlook to be running on your computer to work. Also it will reply to every message you receive from someone - the standard out of office assistant only sends it the first time you get a message from someone. Could cause an interesting loop if two people have the same rule set.