Again, there are several possible ways to accomplish the "final goal", by using different setups and/or using different tools (and/or tolerating some minor inconveniences when booting to "another" OS).
The "hide" from other OS is one of the possible approaches.
I personally believe it to be inconvenient and prone to errors, and have always set multiboot systems in such a way that everyone sees everyone else (within the limits of filesystems supported).
In the case of the mentioned OS's the setup "I see you all" is perfectly possible, but in practice the limitations of each OS (without using particular third party tools where available) will lead to a "telescopic" view.
- DOS 6.22 can access only FAT12/16 filesystems and only within a range on a largish hard disk
- DOS 7.x (and Win9x/Me) can acces only FAT12/16 AND FAT32 (still within a range on a largish hard disk)
- NT 4.0 (not cited) can access FAT12/16 AND NTFS, BUT NOT FAT32 (I know it was not listed, putting this just for the record) also with limitations in sizes/addresses of partitions
- 2K (not cited) can access FAT12/16 AND FAT32 AND NTFS, (BUT NOT exFAT)
- XP can access FAT12/16 AND FAT32 AND NTFS (AND exFAT)
The "traditional" way I personally used for a long time on my systems (single disk 30 or 40 Gb, "Win2K centered") has been (JFYI):
C: 1 Gb or less DOS6.22 and DOS 7.x and NT 4.0 (Primary - FAT16) + Win2K "minimal recovery" + Later OS loaders (NTLDR+NTDETECT.COM+BOOT.INI)
D: 2 Gb or so Windows 95 or Windows 98 or Windows Me (Volume inside extended - FAT32)
E: 2 Gb or so "Common DOS Data" (Volume inside Extended - FAT32) <- but I had the Sysinternals FAT32 driver for NT 4.0
G: 5 Gb or so Win2K "Main" (Volume inside extended - NTFS)
H: 5 Gb or so Win2K or WinXP "Test System" (Volume inside extended - NTFS)
S: 1 Gb or so "Common Swap" (Volume inside Extended - FAT32)
F: 5 Gb or so "Common NT data" (Volume inside extended - NTFS)
I: 5 Gb or so "Temporary data" (Volume inside extended - NTFS) copy of data ready to be backed up
*: (variable) the rest, to be mapped as one or two Primary partition to try strange, new, OS's
The above - which is seemingly complex - can (could) be achieved without particularly complex procedures or sophisticated tools/bootmanagers/etc.
I personally find that having the same volume always having (if accessible/mounted/mapped) the SAME drive letter prevents (actually makes less probable) that by mistake you do on a given volume something that you may later regret thinking that you are operating on "another" volume because you are booted on "another" OS with a different drive letter assignment.
But this is just me.
Such a configuration (if properly setup) is stable, and - anecdotal evidence at it's best - it has been running for several years without a hitch.