How can I improve??

[rbutcher]

Here are a few pictures I have taken at swim meets. My camera is a Canon XSI with a canon 70-300mm IS lens attached. My problem is stopping the action with very little light. These are taken from the stands as we are not permitted on the swim platform. Any suggestions are appreciated. And also the stock flash on the camera is limited to distances. And I believe I have hit the limit that the stock flash will allow. Would a 430 ex II or 580 ex II allow for better results? The distance at the most is around 100 feet maybe 150 feet away at the most. I am getting better with each meet however I think there are bigger improvement that I just don't know yet. Thanks for any help.
OK pictures uploaded. After figuring out what was wrong. Please comment as I am a new to this level of camera and looking to improve. It has been very rewarding thus far. And I hope to pursue this hobby further.

 

[molsen]

I like #3 a lot, but the white balance is off a bit (a little too green) and the sharpening is just a bit overdone.
1 & 4 are underexposed and the color balance is off (too much magenta and blue)
#2 has good white balance and color balance, but I'm disappointed his arms are cut off. Would be an awesome shot otherwise.

an external or hotshoe flash would definitely give you more power than the on-camera one. a lens with a wider maximum aperture would be ideal, but costly. a flash upgrade would be much cheaper and would be useful in all realms of your photography

 

[rbutcher]

Thanks Molsen. Yes I would love to have some better glass. And I do plan to upgrade as I learn more. What suggestions would everybody have for the settings I should use on the camera(XSI) for these types of pictures. I just want to know if this is as good as I can expect from this 70-300mm IS lens. As I said I am very new to all of this and learning each time I use the camera. I am having fun working with the camera and I think this hobby is going to start costing me a fortune as I want the best pictures possible. How much better can I expect from a 2.8 L series lens?? I am also learning how to get the right angles for better pictures. But it is a challenge with the light levels and working from the stands at these meets. I will get better and please any information anybody wants to share will be appreciated. I am like a sponge right now trying to absorb as much as I can.

 

[Wyjid]

underwater housing and a scuba setup.