Hi BlackSun,
You're right, there's no option to hide the DOS window!
This functionality is present in the new mGalaxy version (as you can see in this code extract from the systems.xml file)
<System type="Arcade">
<Name tgdb="Arcade" gb="84|ARC">Multi-system [MAME]</Name>
<Emu selected="0">
<Cmd id="0" hidden="true" name="MAME" value="-rompath "%path" %file%ext -volume -%volume(32,0) -skip_gameinfo -nowindow"/>
</Emu>
<Extensions>.zip,.7z,.chd</Extensions>
</System>
You now have a 'hidden' parameter to hide the launching process for SOME application (because some (rare) others don't like it)
So, sorry, you'll have to wait for the next mGalaxy version release! Thanks