Here's how PowerPoint's help says to do it. To reproduce the information
below hit the F1 key in PPT and type "changing ruler to cm" in the search
window. Select the top item that appears (in PPT 2003):
"By default, the ruler in PowerPoint displays measurements in inches. If you
want to view and work with centimeters, you must configure Microsoft
Windows. You cannot change the measurement units directly in PowerPoint.
1.. In Windows click Start, and then click Control Panel.
2.. Double-click Regional Options or Regional and Language Options.
The options that appear are different for each version of Windows:
a.. If you are working in Windows XP, click the Regional Options tab,
and then click Customize. On the Numbers tab, in the Measurement system
list, click Metric.
b.. If you are not using Windows XP, look for a Numbers option that
includes a Measurements setting, and then change the value to Metric.
3.. Apply the changes, and then start PowerPoint.
The rulers will now display measurements in the system that you have
chosen.
Tip To change back from centimeters to inches, select U.S. from the
Measurement System drop-down list."
So when I read all this it looks like you need to change the regional
setting to U.S. to get the inches.
Hope this helps, let us know.