I can now view HD video on my 'not quite so ancient now' Win XP PC.
I've bought a used 3GHz motherboard and processor and updated the drivers for my Radeon X800 Pro video card and can now play my #11 HD video with VLC player and do basic editing with AVIdemux. I'd say that my PC setup is the bare minimum but it works!
I'll be looking for a slightly less basic editor soon! I flew the EZ* this morning and will post some video later for your comments when I've had time to edit it.