You will get a lot of different answers to this question, the best thing
 to do is try it yourself and see what you think.

Scott

Like Scott said, it's subjective.  6MP can produce a good-looking 20x30"
poster if the image was well lit / low-noise.  The more you crop, the
lower the resulting image quality will be; the more you enlarge, the
more noticable motion blur will be; some people will notice, others
won't care.

As a photographer, you'll probably find that you get more picky about
the technical quality of the image, while the kids and parents are
tickled just to have the shot captured.

FYI, Nikon makes 3 versions of their 70-300 lens, which is a great range
for sporting events.  At $135, it's hard to go wrong by starting with
the least expensive version ($15 cheaper if you go with a grey market
version).

http://www.bhphotovideo.com/bnh/controller/home?O=Search&A=details&Q=&sku=207359
&is=USA

Cheers,
Richard

1152x864 Really - I've done some excellent 8x10 photos for publicity shots
at the community theatre.

It would be much better to get the proper lens.

    Again, you do not just look at the number_of_pixel but you have to look at
the whole image.  And I bet you can see it yourself without needing any
answer from other.  Or the whole thing would go like this.

- Pixel-to-Pixel, if you like 8x10 on 3MP then you should be 3 times happier
with 8MP.  Or you should be able to print 3 times larger and still have a
smile.

- Quality-to-Quality, now this is the whole different story.  *If* your
Nikon D50 and 70-210mm can capture a sharp/clear image, then sure you should
be able to crop to around1/3 to have similar quality of the 3MP (or even
better?).

    *But* if it's a poor blurry image then the whole 8MP image may not even
equal to 3MP at closer range and better situation.  That's one of the
reasons why many suggest to for GOOD FAST LENS.

Completely depends on the image and your standards of quality.

An image with no or little detail will hold up bettering to low ppi printing
than one with a great amount of detail.

An easy way to test without going through a bunch of paper and ink is to
copy out a small section of the image and print it at various resolutions to
see where it starts to look bad to your eye.  Now, you know the minimum
resolution for that particular image.  Make sure and copy out a region of
the image that has the most detail in it.

Buy a Nikon digital camera with 55-200mm VR lens.