Hi Mike4UT,
I hope you are doing well. First I would recommend you to check for the latest updates using automatic updates. If there are new codec’s or required codec’s it will be downloaded and installed by the automatic update feature of windows vista.
To access windows updates click on start, click on control panel and then click on windows updates. You will see all the important and required updates.
I will also include the link for our codec package which you can directly download and install.
http://www.microsoft.com/windows/windowsmedia/download/AllDownloads.aspx?displang=en
Use the above link for downloading codec packages for all the versions of windows media player.
I hope this information will be helpful.
Please let us know if you require further help.
Regards
Rehman- Microsoft Support