The executable icon is deliberately generic, as the updater is used by other UIs as well. Could use better icons though :P
As per windows design guidelines, you need sizes 16x16, 32x32, 48x48, and 256x256 (optionally 24x24, 40x40, 64x64)
http://msdn.microsoft.com/en-us/libr.../aa511280.aspx