It is relatively easy to re-size pictures in irfanview with just a few simple steps:
start irfanview select FILE> open. then select the picture you wish to re-size.
The next thing you want to do is crop any unwanted area out of the picture before proceeding: Use your mouse to create a box around the wanted portion of the picture and then select EDIT > crop selection.
Next go to IMAGE > resize/resample and then put in a width and height less than or equal to 640x480.
Then the last step. FILE > save as name it and save select JPG from save as type, and you're done!
http://irfanview2008.org/