Can you give us a bit more info. what make/model of camera. Are you using the supplied driver or some other method (Card reader). You mention email.... please expand what you mean by that. emails from others with pictures embedded or something else.
It could be that your camera is downloading both a full size image and a thumbnail and you are opening the wrong one. One way to tell is to let us know the filesize of the image you are opening. (Right click - properties)
Windows Picture/fax viewer is rubbish. you ideally want a proper photo editor. There are loads , I use The Gimp. its freeware so no 'dodgy software involved. and is extremly powerful in what it can do.
To install it there are 2/3 packages you need.
Do this first
http://downloads.sourceforge.net/gim....6-1-setup.zip
then this
http://downloads.sourceforge.net/gim...86-setup-1.zip
If you want the help files (probably recommended if you are very new to playing with images) then install this as well
http://downloads.sourceforge.net/gim...0.11-setup.zip
There are loads of tutorials for GIMP on the net.
http://www.gimp.org/tutorials/ is one good starting point but there are loads more for when you get more advanced.