Is there really a substantial difference between a 2 Megapixel and 4 Megapixel cameras output if you are only interested in a 5 X 7 printed image? Fillingim

It depends on the type of pics you take and how much quality you are used to see / want to see. Some people can live quite well with 2MP, some others feel like having not enough with 4. It would be best to take a 4MP-picture and take a close look at the desired size (if you have a good one, use your ink-jet-printer), than downsize it via your picture-editing-software to 2MP, do no postwork and print it again at the same size. Than compare the two pics. If you have a pic with lot's of fine details, you'll notice the difference, but if this still is good enough .. your decision. But keep in mind, that you may take one excellent shot one day and you may want to print it bigger .. ;) Just my 2 ct. :)

From an article "More Is Better" Megapixel Math, A Buyers Guide To Understanding Digital Camera Pixels." May/June 2000 The chart is one I worked up myself using the data from the chart in the article. I hope this helps. Can go into greater detail, with in-depth explanation if you need me to but this chart is pretty self-explanatory. As Raven said it is all personal perception of what makes a decent print, but more is always better.

Wow...Thanks guys!!! Fillingim

...and also, do you make prints or view on the computer screen... or always use full frame, or use "digital zoom"?

Michelle's info is correct to a point. This data is based on an out of the camera image. There are ways to increase size and print quality to an extent. If you think of all columns shifting to the next higher value with about an hours worth of work you can get the idea. There is a limit however, perhaps MAYBE 2 size increases before quality noticeably starts to deteriorate.

Depending on the content of the pic, the visible loss in quality can happen a lot earlier. Remember that you just simulate information, that's not really there (in contrary to analog photography). Just adding that to zhounders true words. Also, keep in mind that there are other important things on a digicam. If the lens is trash, it's of no importance if 2 or 4 megapixels digitize that ... ;)