Auto response is not available in Entourage as far as I know. I'm not sure about Outlook Express. We have entourage in our office and when employees take vacations, I set up an auto-response message at the mail server. This may not be an option for you though. Who is your ISP? Does your company have it's own domain name? You may have mail forwarding in effect and could possibly do something at that level.
[OSX 10.4] [Dual 2.5 Ghz G5] [2 GB Ram] [Dual 17" Monitors]
"Since you like chicks, right ... do you just look at yourself naked in the mirror all the time?"