I am really tired of DLing a Rom and missing 10 files.... am I doing something wrong when I DL?
The version of the rom has to match the version of MAME you are using.
Things are renamed and reorganized between versions, so the current version of MAME can't find them in the old rom
and an old version of MAME can't find them in a newer rom. (if changes have been made, if not it will work fine)
one site has MVC2 as an official mame game... I am assuming to get this to work I have to figure out another damn emulator? NullDC?
Not every game that has been dumped into the MAME romset is playable in MAME. Yes, you will need a different emulator to run MVC2.
I'm not sure where NAOMI emulation is in NullDC.
Demul would use the rom from the most recent MAME romset (or slightly older if no changes have been made to the rom).
I'm using Makaron for that game, but it's far from a user friendly setup. (and it uses a different rom)

Hang around long enough and you'll start to understand how it all works.
I have just about everything possible on my setup, but don't spend much time playing the games.
Getting things to work
IS the game for me.