Unfortunately it can't be done natively with Powerpoint. You can display just the slide number using Powerpoint's built-in capabilities, but not display a "Page x of y" type of count.

There's an add-in for the 2003 and 2007 versions of Powerpoint that will accomplish this, but I have not seen one for 2010 yet.

Best recommendation is to figure out how many slides you have, and edit the Slide Master:

1. Click on View.
2. Click Slide Master.
3. For each type of slide that is being used in the presentation, click on the slide type on the left.
4. Click on the right-hand footer box, and add " of y" after the "<#>", where y is the total number of pages in the presentation.
5. Close the Master View.
6. Click Insert.
7. Click Slide Number.
8. Under the Slide tab, put a check next to "Slide number" and click Apply to All. If it was already checked, uncheck it, Apply to All, then recheck it and Apply to All to get the new Slide Master information.

Hope this helps.

-SW