Paul Sokal - Dallas, TX , Dec 13, 2006; 07:51 a.m.
Not sure exactly what you're asking or why. When you camera captures an image the pixel count is determined by your sensor. So a typical 6 megapixel sensor is 2000 by 3000 pixels. This is a "permanent" characteristic of that file unless you crop out some of the pixels. The size of the final image as a print or on your monitor is determined by the pixels per inch you choose to output the image so at 300ppi the image would be 10 inches wide (3000/300). So ppi is like changing the volume on your stereo. It is not a characteristic of the image file but of your output medium.
Now why in the world would you want an image at 1000ppi? most people can't tell the difference below 240ppi without examining a print at close range with a magnifying loupe, and certainly nothing above 360ppi.
The reason your file gets smaller with saving is that you're saving as a jpeg and with each save, you get another round of jpeg compression and image degradation. Save as a PSD of TIFF and this won't happen.