Windows 7: Getting MPegs from You Tube to appear?

I have downloaded some music videos from You Tube and put them into a folder inside the default Video folder in my docs. When I go to the media center and try to get them to appear for some reason the videos which appear as Mpegs or MP4 in the folder wont appear in the media center and therefore I can't play them.

I have tried to add them to the media center by getting the media center to search for them but although the folder appears the files inside don't do you know why this is and what if anything I can do about it?

The problem is now solved! I looked around on Google and sure enough it lead me right back to this god send of a forum.

This forum is the business, I have been on other forums where even the 'more' knowledgable forum members either don't know what they are talking about or they don't like to divulge their info.

From the few times I have been on this forum I have found the advice to be second to none, is this forum run by or do Microsoft contribute to the running of this place?

Windows media player won't list mp4 files