You can do this by creating a rule in Outlook, but it does mean you have to leave your computer and Outlook on as the rule will only work when Outlook is running. You will need to create a template as well.
Past experience has meant this is not totally reliable either sadly but, that could just be the infrastructure we had! You'd have to try it yourself.
Create template - Open a new email, type if your message and subject and then click save as. Save it as an Outlook Template file
Close it down and return to Outlook.
Click on the Rules and Manage Rules
Create a new Rule
Start from a blank rule - Apply rule on message I receive, Next
Click Next without checking anything
Click yes to the pop up box
Reply using a specific template
And "next" to the end and save
(Don't forget that it wont' turn itself off automatically, you'll have to disable the rule when you want it to stop)
However, if you are have an email account, you are possibly using something like Gmail, Live, Outlook, Yahoo, GMX etc. All of these allow you to set up forwarding/out of office responses on the server (where you log on to your web mail)