MAME = Arcade, and all of these special sets (Naomi, Taito, Neo Geo, etc) are all Arcade games. Every single one of those roms is already included in a MAME Rom set, which just got updated to MAME .183. You can manually pull out the games you'd want to create a seperate set of games, or you can find them pre-compiled online. As far as what Derek was saying, as of MAME .181 or .182, the Dreamcast BIOS were changed (which is what Demul uses, even for Naomi). It used to be that it was all in 1 file, dc.zip, which is what Demul wants. Now, MAME has split that in to 3 different files. You'll need to take the files out of the 2 new zips and put them in the dc.zip, or download a MAME non-merged romset which has a correct dc.zip. However, a split romset (the standard set that has 3 dreamcast bios files now) is much much smaller than a non-merged rom set. Non-merged is much larger due to every variant of file has everything required inside of each of them. It's a combination of split and non-merged. MAME is kind of confusing, so I don't blame you.