If you have a late(ish)-model digital camera, preferrably around 4 megapixel or above, you should be able to take photo's at (at least) 1024x768 in hi-res. Try looking in your camera's settings to change to what you need.
You'll know when you have the right setting, because the shots take a little longer to snap/complete. You may also need a tripod or a steady object to rest your camera on, and perhaps a cable shutter release to avoid shaking your camera ~resulting in a blurred shot.
Changing your photo in photoshop to a larger size than what the picture was originally taken at will most likely result in some distortion etc, and often will take considerable work and effort to correct.... but it is possible to achieve good corrective results with hard work and patience.
I'd suggest doing a google search for tutorials on the exact subject/result you're trying to achieve. There are literally thousands out there on the net. 