Actually if they are good images, the 1024x768 images should print reasonably well when cropped and printed 4x6 (682x1024pix@170ppi). They may not be quite as sharp as some printer & paper compbinations can deliver when fed higher PPI images, but the difference will be rather small.
Try them and you'll find out Ming. I'd say the 1024x768 will probably be acceptable but it is subjective, seen on it's own it'll probably look fine but against a better resolution print it will likely be wanting
Upsampling in a programme like Photoshop will improve the prints if done properly
Thanks guys! I made the mistake of resizing my image to 800byXXX or 1024byXXX with photoshop, the reason for that is, the image will fit the monitor better when posting picture in my website... now when it comes to printing, hmm... i shall suffer~
Comment on my photos are welcome!! I am truly a amateur in photography, I bought my first camera(Pentax S4) in April of this year! So not even a year with camera experience!! But I really love taking picture now, read alot about photography, and love the picture posted in nikonians.org and pbase.com!!
Orginal pictures should always be saved unmodified and unedited. From the original images it is easy to do WEB versions and print versions. Here is simple chart that roughly tells what resolution is needed for high quality prints.