Free & Fast Photo Resize that you can install on your girl-friend's laptop, or your granny's desktop.
Step 1: Download and install imagemagick from http://www.imagemagick.org/script/binary-releases.php#windows
Step 2: create a resize.bat file on the desktop, with the following line and save it.
for %%x in (%*) do convert -resize 800x600 %%x "%%~dx%%~px%%~nx_800x600%%~xx"
(OR, you can download resize.bat from this project)
Step 3: now you can drag and drop one or multiple files to this resize.bat, it will create resized photos in the original folder with _800x600 in the name, say your photo is d:\a.png, the resized will be a_800x600.png
That's it!