Windows 2.10 can be run from DOSBox's native DOS environment,
but some version number trickery must happen first.

Windows 2.10 has the same problem as Windows 1.0, you see,
where if you run WIN.COM on MS-DOS 5.0 or higher, the boot
screen appears but then it spews a screenful of garbage and
crashes. This does not happen under MS-DOS 4.0 and earlier.

To avoid the screenful of garbage, you must type at the
command line before running WIN.COM:

ver set 3 30

This tells DOSBox to report itself as MS-DOS 3.30, which
makes Windows 2.10 happy.