emulator not showing in adb devices

Make sure that you are at the path and give command.

android-sdk_r12-windows\android-sdk-windows\platform-tools>adb devices

I am also using win7 64 It is working for me. If you are getting any error. Mention it.

Also make sure that USB debugging is enabled in your device.

Settings>Applications>Development>USB debugging

Can you able to see device in eclipse? If not then close your emulator and open it again.

You can also try to :

 adb kill-server
 adb start-server

to restart the adb server. Maybe something went wrong with the adb-server. This happens a lot, and many such issues can be solved by restarting the server.