Being a bit dense.... I suspected that Direct 3D version 8 was working but version 9 resulted in stuttering.
What I realise now is that if the version of Direct 3D isn't intalled, then Mame reverts to GDI videomode.
So safe to say, Direct 3D just doesn't work with Star Wars on my set-up. Shame and not sure why - is this a bug with Mame or just my set-up?
But GDI and Direct Draw do work. Of the two, I think I prefer GDI - the vectors are just a bit too 'fat' when using Direct Draw - despite playing with settings to reduce their size.
Hope this is of use to someone else....