Guidance needed

OK, so I have been taking pictures of my daughters U15 soccer games, well two games so far. The games played during the day are not a problem. It's the games that start at 7 p.m. that I could use some advice. I have a D5100 and a D200 for bodies. My two lenses are Tamrom 70-200 f2.8 no vc and I also have a Tamron 70-300 w/vc. What would be the best setup/settings for these night games? These might be vague question but any input or suggestions would be extremely helpful and appreciated. I am a little intimidated with low light and now throw in sports..........ugh.

Low light equals fast lens. I would use the 2.8 because you will need to capture as much light as possible. You will still have to up your ISO but not as much as the 70-300, which I am assuming is a slower lens.

Well, if it were me, I'd try to get there early and stake out a good spot in advance. It sounds like you don't have a tripod so you'll be shooting off-hand, correct? I'm assuming you will be. I'd take the 70-300mm, put the aperture at f/5.6 and meter the scene. If I could get away with a smaller aperture, so much the better but my point here being... I'd let the ISO go as high as it needed to keep my shots at 1/60s or faster with an aperture in the f/5.6 range (notice I said "range"). At 200mm your depth of field at f/2.8 is going to be miiiighty slim, probably around 6" or so if I had to guess and even less at 300mm, so I'd avoid going really wide as much as possible. I'd also use a tripod if I could...

Creatively speaking don't get hung up on the idea that every...single... shot... needs to have absolutely crisp stop-action; a little motion blur can be a nice dynamic for sports shots like these.

If you do have one, a monopod would help.

EDIT: Ah yes, i see you have one..
That could help with the 2.8 lens

For events like this, I would also suggest setting your auto-ISO so that it will give you can set the minimum shutter speed. That way you'll capture the action rather than capture the blur. That said, sometimes the blur looks pretty cool but having them all blurred might not be as cool. It's better to choose which to be blurred and which not. In addition, you can achieve that blurred effect with PS, so even if they all come out sharp you can turn a couple of them into blur if you wanted.
Also, consider setting your camera up for panning shots. When a kid is running directly in front of you take the auto-ISO off, stop down the lens and then make a pan of the kid and ball as they pass by you. Panning takes a lot of patience and practice to get it right so try making lots of them and hope a few come out.

I have been shooting some freshman football games lately that start at 6 PM and run until about 8 PM. I am using a Nikon 70-200mm f/4 and a Nikon 70-300mm f/4.5-5.6 both with VR. I have been using shutter priority mode with the shutter set to 1/500. I start the game with the iso set to 100 or 200 depending on the light and then increase the iso as it starts getting dark. At some point I usuallly switch over to auto-iso since the lighting becomes a little inconsistent. I personally have found that using my D7100 without a monopod and VR on seems to work better for me than with a monopod and VR off. Since I am shooting from the stands I have been using the crop mode on the D7100 which makes the 300mm a 600mm equivalent.

The slowest shutter speed I could shoot at was 1/320 (ISO 4000, ~f/5, D7100, 55-300 mm VR, handheld but seated) for a football game under stadium lights outside. Any slower shutter speed and the blur was a train wreck. You can see those photos here: http://nikonites.com/sports/16648-homecoming-game.html#axzz2fCvSBB8l

You will see there is a small bit of motion blur, but completely acceptable. The other thing was at the time I was shooting the pictures they looked like complete crap on my lcd. Much better on my computer and then I did my editing.

Thanks for the info. I have gotten some good starting points. I will take both cameras and see what I can do.