It's not terribly difficult, as Visio can be linked to a number of data sources (it was originally designed for visualizing data in Excel). Google VisioGuy for a look at what Visio can do - and it's a LOT more than you're thinking. I've seen some rather amazing stuff.

If you really want to make Visio sing, delve into the ShapeSheet. Anybody who has programmed an Excel spreadsheet will pick it up in no time. The tricky part is there are a lot of properties and different objects can have different properties and knowing what does what takes some research and practice.