I have a Canon D40, and have a few issues that I cant seem to figure out :)

1) When taking pictures indoors, my pics have a yellow feel to it. almost like using a yellow filter effect. How do I fix this?

2) When using my 400mm lens, it gets very pixelated at the long end of the zoom. Why?

3) When using my built in flash on portrait pictures, I get bright spots on the skin, and the skin becomes darker than it really is.

I have tried different manual settings, but just cant seem to find the right setting to fix any of the above problems

Thanks for the help