PowerPoint 2010 allows users to set the screen resolution for a presentation. The screen resolution will be used during the full screen slide show.
Specify screen resolution in PowerPoint
Users can specify the screen resolution using the option available as part of Slide Show menu. Click the Slide Show menu in Office Ribbon and navigate to Monitors section.
Then click the drop down for Resolution and select the appropriate monitor resolution for the full screen slide show.
Please make sure to the select a resolution supported by the projector and the most common resolution that is supported in 1024×768.