I'd like to switch from FreeBSD to NetBSD with the possibility of a
speedy backout.  Are there any hitches to simply leaving my DOS
partition table, FreeBSD disklabel, and FreeBSD filesystems intact,
and installing NetBSD over them?

In more detail:  I have 1 DOS-style partition taking up the whole
disk, which is partitioned as follows:

8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  a:    65536        0    4.2BSD        0     0     0   # (Cyl.    0 - 4*)
  b:   524288    65536      swap                        # (Cyl.    4*- 36*)
  c: 12675222        0    unused        0     0         # (Cyl.    0 - 788*)
  e: 11560960   589824    4.2BSD        0     0     0   # (Cyl.   36*- 756*)
  f:   524248 12150784    4.2BSD        0     0     0   # (Cyl.  756*- 788*)

a = FreeBSD root, e = FreeBSD /usr, f = FreeBSD /var.

The NetBSD install floppy can mount these partitions.  fsck likes them
fine, except for FreeBSD's value for maxfilesize, which is 1<<39.  I'm
not sure what the significance of this is.

So, my plan was to move everything on my FreeBSD /usr partition (which
has plenty of free space, out of the way, and install onto that.  That
way I can easily copy my FreeBSD stuff out, and I'll still have a
FreeBSD root partition if I need to back out.  All I'd need to do is
swap between FreeBSD and NetBSD boot blocks.

One hitch with this is that sysinst seems to want to fdisk, partition,
install boot blocks, newfs, and install software all in one shot.
Obviously I don't want to do all that!  I thought I might just use the
``install packages'' option to install kern and base, but I'm not sure
whether this will leave me with a half-assed install or not.  (I've
never installed NetBSD before.)

Any thoughts much appreciated.  

-- 
``Suppose you tell me when you first began to hate the telephone.'' 
  ---Ray Bradbury, ``The Murderer''
``Your ticket is being printed.  Please take your ticket and keep it
with you ... ''  ---a machine on the San Francisco Municipal Railway