Yes, there is. The N64 emu on Gamecube much like the NES emu is not homebrew. Rather is was extracted from Nintendo's own games; the Zelda Bonus Disk and Animal Crossing respectivly. As a result compatibility is very low but the games that do run run perfectly with improved graphics and sound. As for building the emu with roms, all I know is that CubeSoft Phoenix lets you stream them via PSO and the BBA. Just discovered that Phoenix generates a file called N64.iso as it trys to stream. You could probably burn that file to a DVD (or make a multiboot) to use it.
To WOWchamp: There are also nearly perfect emus for N64 for PC and Xbox. Just because its not possible on PS2 or PSP doesn't mean its not possible at all.
Edit: Theres a N64 emu for PSP now. Oh well.