When you get really comfortable with Visio, consider presenting your diagram as a Visio diagrambecause you'll be able to instantly calculate properties for the diagram. For example, you could assign cost or labor properties to the various intervals, and have the totals put into an Excel spreadsheet. To use the Visio diagram natively, create a hyperlink to it from your PowerPoint slide, and have it open in Visio.
Another option is to present the data in Visio concurrently with your slide show, and Alt+Tab between the two programs as needed. With this method, you can use Visio as a simulationthat is, by changing the values of certain custom properties, you can show the results in a table, presenting a "what if" set of scenarios.
But these are advanced concepts. For now, the best thing to do is to get comfortable learning the basics of Visio by using some of the templates, such as the extraordinarily helpful timeline diagram covered in this article.
Tom Bunzel's latest book is Sams Teach Yourself Microsoft Office PowerPoint 2003 in 24 Hours (Sams, 2003, ISBN 0672325551).