The program I find that's very easy for staff to work with is the Image Resizer Powertoy (by Microsoft Surprisingly). A simple right click to resize images. MS didn't release the same tool for Windows 7 yet, but someone has made a copy of the original.

Download Here (XP): http://go.microsoft.com/fwlink/?LinkId=211477

Download Here (Win 7): http://imageresizer.codeplex.com/releases/view/82827