what is the example of Fast shutter speed for sports photography?

Actually any shutter speed beyond 1/4000.
shutter speeds of 1/8000 are ideal for action photography.

thanks for the info. can you share with me what settings to use on my canon digital eos. i also just have the regular 18 55 lens. i am looking into buying the 200 lens.
thanks

if i use 1/4000- 8000 then my pictures are very very dark and grainy. What can i do about that?

Look there is a tight relationship between shutter speed, ISO (which causes those grains or digital noise) and aperture value. So if you go for high shutter speeds like 1/4000 you have to maintain a wide open aperture as well. At this stage you should have also an ISO of 50 or 100 depending on lighting condition. But it’s not usually possible to shoot fine photos in low light since you have modify ISO and grain or noise will show up on your images.

I have a Nikon D50 with a 70-300 lens and am presently photographing athletes for an exhibition I am having next year, where I'll be using the photos as reference material for painting and sculpture.
Last week for example I was photographing divers (not the deep sea kind!) at a low lit swimming baths. I had my camera on the 'moving image' setting with continuous shutter speed and got a few okay shots. But as the comment Daz made above, a lot were grainy. When I tried to manually adjust the ISO and shutter speeds above because of the low lighting my photos were practically black.How do I get better shots. Do I need external flash equipment?
Amy