When I right click on the picture in Explorer and select send to and then select mail recipient, it offers to make the picture smaller. I don't know if another program added that to Explorer though.
There is a free program (very basic but for $10 you can get a better version) at http://www.showyourphotos.com/photoresizer_free.html
called Photo Resizer. Using the program you open your pic, click on resize (with a few options though the default is fine) and then you can save or email the smaller version. You can do this for one or several photos, adding it to the email as you go on.
A good reason to resize is not only so the pic fits on the email or screen nicely, but also it is a smaller file to email and easier for a dial-up user to download.