I have some NES roms, if someone is interested...

*bump*
This would be crazy.  It must be done.

and possible, IMO. Man, though, it would be even nicer If we could get a gpu somehow. Then, star fox might even be possible!

Not necessarily.....Super FX could cause many, many headaches, and does even on systems with a decent gpu (speaking of handhelds, not pcs)

I wonder how the screen size will be accounted for....

NES, I mean, compare the huge NES screen (your T.V.) to the little screen of the nspire. I assume the game screen will have to compacted.....

wikipedia quote:

The standard display resolution of the NES is 256 horizontal pixels by 240 vertical pixels.

Most older systems had 320x240 or less, even the SNES had most games at 320x240. Only a few games (like Secret of mana) used 640x480, and we could compress the screen for those few.

Edit: here's wikipedia's listed resolutions for the SNES, interlaced and progressive

Progressive: 256x224, 512x224, 256x239, 512x239
Interlaced: 512x448, 512x478

So, some games will not quite fill the screen, some will need to be compressed.

Edit2: Oh and BTW, while NTSC officially supports 640x480, most TVs cut it off a little short so there are no black bars, and game designers usually choose something around 512x384, or a near resolution. This overscan rule doesn't apply to lcds, however.