APDaddy gave you some basic info, now get ready for some longer explanations and math
(if you ever really wanted to know what pixels, dpi, and megapixels mean).
A megapixel is actually a bit more than 1,000,000 pixels. What does that mean? Pixel is a "dot", a smallest unit of the picture that can be only 1 color. The more pixels, the bigger picture, and the better picture is (more pixels = more different colors, for purpose of simplicity - I'm not going to go into color depth, etc). How all of this relates to viewing images on screen and printing them: ready for some math?
If your camera is, let's say, 1.3 megapixel. What does it mean?
Usually 1.3 megapixel camera will take 1280x1024 pixel pictures (here comes the math: 1280 times 1024 is approximately 1,310,720 thus about 1.3 million pixels, or 1.3 megapixels). Average 15" monitor will be set at 800x600 pixels, 72 dpi (dots per inch) resolution, and it's dimensions will approximately be 11.1" width by 8.3" height (close to 15" diagonal). Your 1280x1024 picture @ 72 dpi (that's how monitor will display it) will look HUGE on screen - it will be about 17.8"x14.2" - larger than monitor's screen. It can be made smaller for viewing on screen, and will look awesome.
Now, let's say, you want to print the same picture. Paper has higher resolution than monitor does - that means, paper can effectively display more dots per inch than monitor does (modern monitors can normally/usually display only 72, 75 or 96 dpi - dots per inch). When you print pictures on paper, you want to print at a minimum of 360 dpi, but 720 or 1440 is better. The more dots per inch, the smoother the picture will look when printed. So, back to your 1280x1024 (1.3 megapixel) photo: If you don't enlarge it (and enlarging reduces the quality, as you cannot create something from nothing), and want a quality print, the optimum size to print it at would be:
1280 divided by 360 = 3.5"
1024 divided by 360 = 2.9", so that makes it 3.5" standard photo print at most.
(printer's resolution is a whole another topic, and I'm not going into that, so for simplicity
photo resolution should be about 360 dpi for a good quality print, and printer can be set at 360, 720 or 1440 dpi - higher would be an overkill).
3.5" at most... doesn't sound enough, does it? Ok, let's say you want to print good quality 5"x7" photos.
This translates to:
5" times 360 dpi = 1,800 pixels width
7" times 360 dpi = 2,520 pixels height
1,800 times 2,520 = 4,536,000 , or close to 4.5 megapixel. Good quality 4 megapixel cameras cost a looot
But actually, 3.1 megapixel would make *fair* 5"x7" printed photos.
Do you feel like a digital graphics expert yet? <GRIN>
BTW, megapixels is not the only thing you have to look at. Take a look
http://www.steves-digicams.com - it's by far the best digital camera review site.
thus for me a 2.1 megapixel image does not produce a good enough 8x10 (4x6 - yes, very very good quality better than many 35 mm cameras, butnot 8x10). But, once again - I'm picky 
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