You should not delete windows media player registry files. Now follow this:
start -->> set program access and defaults -->> Click "Add remove windows Component" -->> In windows component page check "windows media player" -->> Click Next
Insert windows XP CD when asked.Complete the process and restart your windows.
You don't need to uninstall previous version of windows media player to install new version of media player. Download latest version of WMP from here:
http://www.microsoft.com/windows/win.../download.aspx
Now, just run the setup, nothing else.