I did this a while back on the Droid X, but I just realized it would probably work on the Xoom — and it does!
You can play any of your old NES games on the Xoom (or any other android phone/tablet, probably), using the Wii remote to control them. There are two apps required to make this happen:
1 – Wiimote Controller: This is a free app that connects your Wii Remote to your Android device via Bluetooth. You can find it in the market here for free.
2 – NESoid: This is the app that actually runs the games. You’ll need to find and load your own NES rom files, though. It has a lite version available for free, or a paid version for just $3.98.
Here’s a quick video of it in action:
In the video I mentioned the HDMI output from the Xoom, which you can read more about here.
There are other emulators you can get (Super Nintendo, Genesis, etc), but the Wii Remote works perfectly with NES games because of the button layout, and I simply prefer those games anyhow.
If you have any kind of Android device and a Wii Remote, give it a try!
