I don't use Windows so I can't tell you how to accomplish this task with the software you have available. However, I've rescaled a number of shows so they play on my standard 4:3 NTSC television. For anime in the 4:3 aspect ratio (mostly older shows these days) rescale to 576x432; for HD shows in the 16:9 ratio rescale to 576x324. Then use the software to drop these videos onto a 640x480 black box. You might need to tweak these dimensions a bit depending on your television.
(I use mencoder
in Linux to accomplish this; it does the entire task in a single step using the "scale" and "expand" filters. There is a version of mencoder for Windows as well, but it's a command-line program, not one with a graphical user interface. There are a number of graphical "front-ends" on the page I linked to, but I don't know if any of them are for Windows.)