Switch between Powerpoint and Excel

I am currently writing a presentation which involves me switching between PowerPoint slides and an Excel spreadsheet designed to demonstrate. I know how to launch Excel from PowerPoint (by simply attaching a command line to the particular icon), but would like to be able to launch PowerPoint from Excel. Not simply the basic application, but to return to the point in the slideshow where I last left. If I'm lazy, I'm sure I can do this with ALT-TAB but I wonder if there was a neater way to do this? I'm pretty comfortable with VBA, and I know there is a line to launch applications generally, though I'm looking to return to a particular point in a slide show (the slideshow application won't be closed, because I'll simply click on an Excel icon to launch the particular Excel file).

Hope someone can help.
Peter