In PowerPoint 2003, this option was located under Format Picture however the latest version has moved things around. To access the alternate text . . .
1. Right-click on the image.
2. Select Size and Position.
3. Select the Alt Text tab.
4. Make your changes to the Alternative text.
5. Click the Close button.
NOTE: In Word 2007 this option is under Size and in Excel 2007 you will find it under Size and Properties.
