Need a quick-and-dirty way to resize a group of photographs? Then get this free PowerToy from Microsoft. It's exceptionally easy to use.
Right-click a single photograph or a group of photographs, select Resize Pictures, and a dialog box appears, letting you resize the pictures to one of four sizes: Small (640 by 480 pixels); Medium (800 by 600 pixels); Large (1024 by 768 pixels); and Handheld PC (240 by 320 pixels). When you make your selection and click OK, it will make copies of your pictures in the new size, but leave the originals intact. If you click the Advanced button before you click OK, you can choose to resize the original pictures, instead of making a copy, and you can also only make pictures smaller, not larger--if you choose a size larger than the original size, the program simply won't make them larger.
Note: This download takes you to the developer's site.