If Boxee is your main media interface, you don't have to shut it down to enjoy some old-school emulation gaming. A clever Launcher app and some command line tweaking lets you jump right into Zelda, Mario and other ROMs.
You'll have to hunt down your own video game images (ROMs) and an emulator app for your Windows or Linux system, though the MakeUseOf.com site recommends Mednafen as a fairly compatible emulator app. Inside Boxee, you'll add a repository to pull apps from, then add the Launcher app, which can be configured to launch any program outside Boxee from a standard Boxee icon.
If that was all it took, well, MakeUseOf's post wouldn't be a how-to. Boxee has some issues switching to full-screen apps on Windows and Linux, and the post details how to get around those issues with a light bit of command editing and script making. I tried out the method and did manage to get Chrono Trigger for SNES to launch from inside Boxee, but I lack a collection of ROMs and emulators to verify universal ease of setup. If you dig this clever media centre hack and find success with your own setup, do tell us about it in the comments.
How To Turn Boxee Into The Ultimate ROM And Game Launcher [MakeUseOf.com]