www.irfanview.com - it is a very small download 
but a VERY powerful program.   Best of all, it's 
TOTALLY FREE.

With it, you can actually make thumbnails all 
the same size in batches.  Just plug in a folder 
of images, set the size, create an output folder 
then VOILA!  The quality of the thumbnails are 
decent and undistorted. 

Good luck!