On Wed, 31 Dec 2003 17:45:02 +1030, "Li'l Roberto"

There are several possible approaches here, but you have to work
within the file system support levels of the OSs:

FAT12/16   FAT32   NTFS*    OS

   Yes         No         Old          NT 3.xx
   Yes         No         Newish    NT 4.0
   Yes         Yes        Newer     NT 5.0 (Win2000)
   Yes         Yes        Newest   NT 5.1 (XP)
   Yes         No         No           DOS**, Win3.x, Win95, Win95SP1
   Yes         Yes        No           Win95SR2.xx
   Yes         Yes        No           Win98, Win98SE, WinME

*  NTFS is an undocumented, proprietary file system that can change as
NT versions change, and even within Service Packs of the same version
of NTFS.  Furthermore, NT can take a predatory approach to any "old"
versions of NTFS it sees, automatically upgrading them to the
"correct" version (and too bad if it's a dropped-in HD from an older
NT version that can no longer read its own drive).

That means you have to manage multiple NT-on-NTFS installations very,
very carefully; think partition managers that hide (via partition type
spoofing) partitions and volumes, and be very careful about what is
currently visible when booting NT CDs or diskettes.

**  Really old MS-DOS versions (4.x, 3.xx, older) have limitations on
what they can see, even within FAT16.  Prolly not relevant to you.

Subject to the perils of NTFS, you may be able to share multiple
versions of NTFS on the same system, if not the same volume.  You can
generally share a DOS with an NT on the same volume, and an older
MSDOS version with a Win9x (except for Win95SR2.xx, which is buggy in
this regard and cannot return from "Previous MSDOS" session).

FDisk can't create multiple primary partitions on the same HD, though
once they are there, it can manage them and Win9x and later can cope
with them (NTFS auto-convert hazards apply).  So if going that route,
you'd need a partition manager, and BING would be my recommendation.
You'd need a tool like that to spoof partition types in order to hide
at-risk NTFS volumes from predatory newer NT versions.

Modern BIOSs can boot HDs other than the first, so you can use that to
select between your two physical HDs.  But don't rely on CMOS settings
to hide HDs; Plug and Play may find them anyway, and that could open
the door to inappropriate System Restore "management" and NTFS
auto-upgrade attack.

Both XP and WinME come with System Restore (SR), and both may
spontaneously re-enable SR if their view of the HDs and volumes should
change an any way at all.  When this happens, existing Restore Points
and associated data are generally flushed.  Unless you are rigorous in
hiding all other OSs and volumes from SR-inflicted OSs, I'd recommend
disabling SR, and I wish you luck in keeping SR dead.

Fortunately, SR has no "magic name" overlap between WinME and XP.
WinME creates \_Restore directories on all volumes it sees, and
populates the one on C: with SR data from all volumes.  See
http://users.iafrica.com/c/cq/cquirke/sr-sfp.htm on WinME's SR and
SFP.  XP's SR creates (from memory) "\System Volume information"
subtrees on all volumes it sees, and populates these with data from
the same volume only (far more efficient than WinME).

SR and NTFS considerations aside, the issue of "magic name" overlap
will determine whether two OSs can reside on the same volume.  All
Win9x and NT share the same "\Program Files" name, so that makes
sharing of a volume between any of these a real problem.  

The DOS modes of Win9x (and MS-DOS) are more forgiving, sharing only a
few files in C:\ that you could manage on a copy-from-template basis
to switch between these OSs, or these plus one full Win9x OS.

NT can co-exist with an MSDOS or a Win9x DOS mode without any drama,
other than perhaps swapping \Config.sys and \Autoexec.bat or
preventing the NT from interpreting these files.  If the DOS (mode) is
in place when the NT is installed, the NT installation process should
create an NTLDR-mediated support to choose between these at boot time,
with pointers to both OSs in \Boot.ini

If using new hardware, you might consider a pile of new Serial-ATA HDs
that can be hot-swapped to boot the particular OSs on them.
Serial-ATA's support for hot swapping requires the use of the new
(rather than legacy) power connectors to these HDs.  

If using legacy power connectors, or "normal" xIDE hard drives, you
must physically disconnect mains power before swapping HDs, because
the ATX power "off" does not in fact disconnect the power.  

Note that modern xIDE HDs don't like removable drive brackets, as the
extra data path mechanical contacts degrades the interface below
reliability levels required to sustain UIDE66 or higher modes.

Never turn your back on an installer program