Computer:Dell Inspiron 530.
One hard disk 160Gb.
First wiped using Darik boot and nuke.
Then installed MSDOS 6.21 into first 2Gb (default MSDOS install).
Then installed 6.0.7 amd64 from DVD.
Standard system install only (desktop turned off).
MSDOS detected, Debian installed into freespace, boot menu set up giving choice into Linux or MSDOS.
MSDOS _not_ detected (message output saying no other OS's found so should be safe to overwrite MBR).
However, Debian is (correctly) installed into freespace.