to some degree, that you will need to play with...
click start, click all programs,
point at the icon you want to change, right click
left click properties, left click customize, left click change icon,
look for icons in this file: %SystemRoot%\system32\SHELL32.dll
and that's not the only file that contains icons, just one of them...
double click the icon you want, left click apply, left click OK
now you can start thinking up more ideas, there's hoards of icons in hoards of files...