> hi, is there a guide or a tutorial on how to burn several rom files
> into a eeprom or flash. Is there a "game/file selector" start screen
> that has to be burned in the cart together with the roms or will the
> nes make that automagically?
> thanks for your help
> regards

Hardware wise, I don't think it can be done on large scale without some
fancy logic circuits. Unlike many other "multicarts" where several ROMs
have common bankswitching format, NES has many various mapper chips and
various arraingements (horizontal and vertical mirroring, etc) and at best
you'd be able to build one containing all the ROMs that uses the exact same
bankswitching format and RAM chips when needed.

You could try building one via FPGA and have it load the appropiate mapper
with the ROM and behave like a normal NES cart but FPGA is not exactly easy
to program. Also you'd need to add an SRAM chip both for game's use and for
save games.

The easiest way would be to use a computer to load the ROM, the required
mapper code, and then load them into NES like a real cart. But when you get
this far, you might as well forget about the NES and use emulator instead.