I usually do prints 8x10 and smaller at 300dpi. If your image is already 1024x768 then you can add pixels but that's not the same thing as adding detail. You can't add to what's not there...

In Photoshop, go to Image > Image Size and see how big the image is in pixels. Like I said, I do small prints at 300dpi so you could use the crop tool set for 1800 pixels x 1200 pixels at 300dpi, then you've done two things in one step. Of course this will only work well if your file is larger than 1800x1200.