Ahh ... Windows Media Player. Version 6.4 is a dream: small and uncluttered with decent full-screen controls. Unfortunately, in a totally unsuccessful effort to upstage RealNetworks' RealPlayer, version 7 is a monstrosity. Can you imagine an upgrade to a media player which loses on-screen controls? You can't even use the spacebar to pause movies anymore. They took everything we hate about RealPlayer and rolled it into Media Player. Great.
There is only one reason to download and install Media Player 7, and that is to play variable bitrate Windows Media 8 content. Other than that, Media Player 6 should satisfy most of your video playing needs, save Quicktime.
After installing Media Player 7, you'll probably want to unassociate it with all file types except .wmv files, which are usually WM8-encoded files. Unfortunately, MP7 will not restore your old file associations, so you'll have to choose Media Player 6 manually when you open each type of file for the first time afterwards.
Fear not, for the old media player is always available: select "Run..." from the Start menu and type mplayer2, et voila! If you're feeling nostalgic, you can even run the Windows 95 media player if you type mplay32 instead.
The worst thing that installing Media Player 7 will do to your machine is disable the Fraunhoffer MP3 codec's higher bitrates. Often, reinstalling l3codeca.acm and l3codecx.ax (such as by running the DivX ;-) installer) will have no effect. This is a serious problem if you are into making XDVDs.
It is also important to remember that you can always download the Media Player 6 installer from Microsoft's site: just follow the link for users running Windows 95 or Windows NT 4. As of May 2001, the download is located at http://www.microsoft.com/windows/windowsmedia/en/download/default.asp?pcode=4.