That question was for Hazel of course, but I thought I might as well try it, and IE7 plays the videos fine.
What started off as a straightforward answer has turned out not so straight forward. I tried changing the settings in Opera to just about anything, and it played the videos fine.
It worked with "Play in Opera", "Use Plugin", etc etc..
What I did find, is that the videos usually wouldn't play straight off. I had to either refresh the page, or select one of the other videos, which is the same as refreshing the page I suppose, and then they worked every time.
Another thing I found was two entries for wmv in the Prefs/Advanced/Downloads section. One was displayed by default, and the other showed up when I unchecked the "Hide file types associated with Opera". So I deleted the first one, and still played the videos.
The last, and probably most relevant point is I'm 99% sure this "download codec" popup was one I got last year sometime, and after doing a bit of research on it, it seems to be something needed by Media Player 6.4, which I think comes with the OS and Windows Media Player by default.
I installed it, and it may be one of the codecs that shows up in that second screenshot. It's actually hard trying to find a download for that codec by googling, as I've just tried. You find lots of entries from different forums, as in Andavaris links, but not a direct download.
I dunno if all this helps, or just clouds the issue even more, but if it's the same codec, although it doesn't show exactly the same name, then it's never given me any problems. Just another codec.