It looks like running the yahoo music engine app on win64 isn't officially supported, but here's how I got it to work.
- download the installer
- right click on the ymjsetup.exe and choose the compatibility tab and set the installer to run in compatibility mode for Windows XP.
- make sure that you've run windows media player at least once
- run ymjsetup.exe
- ignore any error messages that might pop-up; let the installation continue
and that should be it.