Have you read the mame help file?
In which a written requrement to run Mame.
When MAME55 released,the neogeo roms was not fully updated and were use as they were in neogeo emulator.
I know that 500 mhz with 128Mb RAM are enough to run these games.You have to be carefull because speed of any game require a hardware to be fully emulate.Fastmame is an emulator which is desingn for such type of metters.