Image size&resolution for contests (not dpreview)

Folks, when you submit your work for contests what size and resolution do you usually use? I resized my image from 4000 to 1600 pi and the resolution is 240. Is that OK?

Another question: when I view my image with Picasa it doesn't look as sharp as with PS. When I open it with Windows Live Photo it looks too dark compare to PS (I use sRGB color space). How can I ensure the contest jury will see exactly what I see with PS?