I find the free image resizer from microsoft is unbeatable if you're using XP. I use others including photoshop and paintshop, but my first choice is always the powertoy as it's integrated in to the explorer shell and you can resize a file in less time and clicks than it takes just to open the file in photoshop. Files are simply selected by clicking in explorer and right clicking to select resize. Multiple files can be resized by using standard ctrl, shift, click techniques during selection.
http://download.microsoft.com/downlo...ertoySetup.exe (small only 520Kb Download)