The default color resolution for your image may be set higher than necessary. If your image only needs 256 colors but is stored in a format that allows 16 million colors, try resaving your bitmap in a format with fewer colors. Gray-scale images and computer generated color images generally don't need more that 256 colors. Black and white line art and text only need 2 colors. Use a more efficient bitmap format.
Some bitmap formats are inherently more efficient in file size than others.
PowerPoint 97 stores images more efficiently than PowerPoint 7.0. If you are still using PowerPoint 7.0, we recommend you upgrade to 97. Increase the ratio of slides without bitmaps to slides with bitmaps. Since slides that do not contain bitmaps are significantly smaller than slides with bitmaps, you can reduce large file handling charges by simply increasing the number of slides without bitmaps in your presentation. Since all the slides are summed together in calculating your allowance, several small slides can compensate for one large slide.