Sounds a bit confusing, doesn't it?

I've created an 'events calendar' in Excel for my local area. Each date throughout the year is assigned to a row.

What I want to do is, when I enter an event for a particular date, then automatically create an entry elsewhere in the calendar for an action to be taken.

So for example, There's an event on the 30th July, so I enter it into the calendar. I'd like to be able to specify that an entry should be made 4 weeks earlier, on the 2nd July, to tell me to blog, tweet or whatever about that particular event.

Can Excel help me to do that and if so, what do I need to do?