IIRC, it's a naming issue. The drive (virtual or physical) that contains your FA files has to be designated FATTACK or something (I'm not sure though). There has to be an option somewhere in DOSBox that lets you name your drives.
Try playing around with the options you get with "intro cdrom" and see if something works out.
I remember that I had a similar issue and got it to work eventually. I'll check how I did it
