what I usually do is I go to paint open the pic
go to image
stretch and skew
and in the top two boxes type in 50
when small enough for you click save and the file is saved in that size
usually works great for me
Irfanview, freeware application is fantastic for resizing JPEG's and all sorts of image files. It is clearly laid out, and althoug not the simplest to use, it is clear and relatively intuitive.
This is the one I ALWAYS use.
The link I have posted takes you straight to the IRFANVIEW website.
I used to use this program to resize pictures for uploading to MySpace, it was recommended by MySpace. Not a bad program, less complicated than Adobe PhotoShop 7.0.