"Missing plug in" does not tell me much. I can't tell what format John's forum software actually uses but I will make a guess that if you install "Adobe Flash Player" extension/plug-in to your browser, you may be able to watch these forum movies. Check to see if you have the Adobie Flash Player installed and if not get it.
If you don't have it, go to
www.adobe.com and on their web page look in the lower right section for "download" and under it is flash player. It should be free.
This "may" solve your problem. Let me know, I don't use Microsoft Internet Explorer so this is all a guess but if you get flash player directly from Adobe it is safe to install and it is something nice to have on a computer.
I hope John chimes in on this too!