I don't know how to resize from 16:9 anamorphic...
I use a program called XNView for all my image resizing, cropping, colour-correcting etc needs - can't recommend it highly enough! (especially because it's free):
http://www.xnview.com/
To "deanamorphise" captures, you can do a batch "convert" operation and add "resize" from "advanced operations". Set the scales to 133% on X and 100% on Y and make sure "Keep Aspect Ratio" is NOT checked. Set the output to JPG, set the JPG quality to whatever (I usually use 90%), tell it where to put the converted files and press "Go". It'll do the whole lot in a few seconds
Since it's a bit of a pain setting the parameters up everytime, you can save scripts with the operations you want to perform during the convert... I have scripts for, e.g.
Resize 720 x 405 - correct aspect ratio of 720x480 non-anamorphic NTSC
Resize 800 x 450 - deanamorphise NTSC, scaling down a bit
Resize 853 x 480 - deanamorphise NTSC, preserving vertical res
Resize 1024 x 576 - deanamorphise PAL, preserving vertical res
All of which also have an "autocrop" operation set up to remove black bars & borders during the conversion

Means I can get captures ready for manual cropping into portrait form in just a few mouse clicks
