The change to Outlook is not hard. It may be expensive though.
Typically, you get Outlook as part of Microsoft Office.
Even with Outlook though, you may not get what you want.
In a typical office, all users are connected to a network mail server such as Microsoft Exchange. When you set an away message for Outlook, you actually place a flag on the mail server to auto-reply to your emails with the away message.
For home or small office use, you would need to leave your computer on, and connected to your ISP, or set to connect to the ISP on a regular interval.
Looking over other alternatives, Pegasus Mail does offer an auto-replay function IF you also install their mail server application.
http://www.pmail.com/overviews.htm
Pegasus is a free mail application.
Chas