Title says it. I've been looking for an alternative to Fceux since it just doesn't work on my computer and I thought: "Why not look for a way to run NES roms in ZSNES?". On my adventure to find the holly ZSNES plugin (if they even exist), I decide to ask ths community. And here I am, asking you how to do this.
ZSNES aside from being a SNES emulator, does not support plugins, therefore a plugin to play NES games on ZSNES does not only not exist, but is impossible.
However, a hack is possible. You will not be getting fixes or updates... however, such hack has been done: Z.N.E.S. To download, you have to remove the "s" from the link in the post I linked to.
Note: You will need to get the Famicom Disk System from elsewhere and place it in the executable folder.
VirusTotal Scan: mostly clean (1 out of 60 engines says it is unsafe).
I tested it with both SNES and NES roms. It works for some NES roms, otherwise it crashes (yes, it crashes with SNES roms). You might aswell get a proper NES emulator.
In my personal opinion, you should look what is out there, instead of trying to make it all work inside of ZSNES. You might even consider other emulators for SNES.
If all you need is a NES emulator because Fceux is not working for you, there are alternatives to Fceux.
ZSNES is a SNES emulator. It can play only SNES games. If you want to play NES games, you need to use a NES emulator, which were made to do so.