I found a clone of Microsoft's Powertoy Image resizer, which I often use to resize pics for posting here or emails etc. MS haven't reproduced this for Vista or 7, but I have this site that has-
Image Resizer Powertoy Clone for Windows
Their definitions of small, medium and large differ, but you can always use the custom size. Just select the photos in Explorer, right-click, Resize images. Presto, it makes copies in the same folder.
I do not have Vista or 7 so haven't tried this one yet, just stumbled across it and thought people here may want it.