Download Image Resizer, to right click and resize images
Image Resizer is a Microsoft Powertoy that creates a new option in the right click menu, to resize one or more images immediately. There appears a dialogue to let you choose between some standard sizes and (advanced) let you overwrite the existing files instead of creating new ones. Excellent, if you don’t want much control over the resize parameters.
MS Image Resizer works only on XP, but you can try a clone of it that was created to extend support to non-XP and 64-bit versions of Windows.