An Auto-Reply filter is probably the best way to go about doing this:
Create a new rule with the following conditions:
select Conditions: "which is an automatic reply
"
select Actions: "Move it to the specified folder
" or "delete it"
I would recommend you use the "Move it to the specified folder" option instead of delete though. This rule will be active all the time and you don't necessarily want all your regular out of office messages (at other time periods) to get auto-deleted. By filtering to a folder, you can then picka nd choose what you do with the messages from then on.