I'm not sure what version windows you are using, I am running windows xp and I use powertoys for windows xp... image resizer, all I have to do is right click my picture and click on resize pictures.. from there it gives you different options of how you want to resize them. to resize more than 1 picture at once. I just hold down the shift key to highlight as many pictures as I want to resize, then right click..
PowerToys for Windows XP
Image Resizer
This PowerToy enables you to resize one or many image files with a right-click.