i m trying to get the best 4x6and 5x7 prints but also my online photo gallery pics dont look so great after i make them 1024x768
This is a normal result of downsizing an image as it takes on a softer appearance (someone else may be able to give you the reason why this happens - has to do with eliminating some of the image detail). Sharpening techniques such as applying an unsharp mask to the image is necessary to restore the apparent sharpness of the image. More or less sharpening may be needed depending on the subject matter and the amount of downsizing. The amount of compression applied in your JPEG images for the web also affect the appearance.
Be carefull with sharpening as it can add its own negative characteristics to the image such as increased noise or halos around the edges of subjects. Normally, prints require and can handle more sharpening than images on the web without adverse effect.
i would be better a a lower resoloution
I think you should always shoot in the best quality available unless you have other factors (memory issues, addtional processing when using RAW, etc.) preventing you from doing so. You should capture the best image possible and process for your prints. What if you decide you need an 8X10?
That being said, you should pay attention to your composition when taking the photos to reduce the amount of unnecessary cropping later to get the image you want. Remember to fill the frame with your subject and if it does'nt add to the image leave it out. Just because cropping is easy doesn't mean its the best way to go.
Hope this helps!