Having Powerpoint update automatically using XML

I am using Powerpoint 2007 to display current and upcoming events on our digital signage in our lobby.  This looks really good, but the problem is that it has to be manually updated on a daily basis which becomes tidious.  Is there a way to create an XML file so that we can add multiple days of information to it, but tell Powerpoint to get certain parts of that information on a daily basis.  For instance, we would create a document that has events for Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, and Sunday.  On Monday, we want Powerpoint to automatically use the events under Monday and Tuesday but not any of the other days.  Follow that sequence for Tuesday which would use Tuesday and Wednesday.