Unless you save the image to your computer, you
really don't have control over its size.
Why don't people resize before they send images?
Because they basically don't know what they are doing.
They think emails can be 10MB in size, so just pile
everything into an email and send it. Who cares? That
is even worse for people still using dial-up.
You will have to educate them. I prefer IrfanView to
handle anything to do with images. I prefer that over
any native program in Vista. Others might prefer to use
Windows Photo Gallery.
IrfanView is freeware. If you decide to try it or recommend
it, be sure to download the Plugins as well.
IrfanView - Official Homepage - one of the most popular viewers worldwide:
http://www.irfanview.com/