MAME/CPS Woes and Troubles

[Skulhedface]

I've noticed as I download a myriad of MAME/CPS/ whathaveyou roms (basically arcade games, ya know?) that a good majority of them fail to work.

The main problem is that the game itself will be listed in the "available" directory, and that I can fiddle with the options prior to starting the emulation, but that when I attempt to run it, it tells me that a bunch of files are not found.

My question is, what's the problem?

Is my computer not catching all the files?

Are the ROM sites only offering partial downloads? (I've noticed quite a few CPS games I've downloaded have this problem... every time I try to run a Marvel vs. SF game, or even something simpler from the old school like Alien Vs. Predator, it won't work.)

Do the emulators themselves not work correctly? Highly doubtful because I have a shitload of different emulators, basically the Windows version of every MAME/CPS/etc emu's I could find from any of the sites listed in the ROM exchange thread.

Any help would be greatly appreciated.