As far as the resolution goes, if you go into "image size" under your image pull down and then uncheck "resample image" the dpi and actual image dimensions will fluctuate around depending on which one you change. If you have an image 1024x768 at 72 dpi, do not have resample image checked and then change your dpi to 300 your image should come out to be about 3.4x2.5 in inches. You will keep the same number of pixels in your image if you do not resample. However if you go the other route and click resample image, have a set width, height and dpi, Photoshop will either reduce the number of pixels if you reduce or interpolate pixels if you enlarge, which can reduce image quality.