Gleaned from stuff David Gatwood <marsmail@globegate.utm.edu> has written, 
here is my recipe for changing mach kernels, Linux servers and system maps 
from Mac OS.

Given:
1. Booting from MacOS 8.5 on an HFS+ disk at internal SCSI 0
   (/dev/sda or call it macos_boot_disk)
2. A second SCSI drive at external SCSI 4 (/dev/sdb or call it 
   mklinux_macos_partition) with the following partition map:

  Partition map (with 512 byte blocks) on '/dev/sdb'
   #:                type name              length   base    ( size )
   1:           Apple_HFS MacOS             409600 @ 1724705 (200.0M)
   2: Apple_partition_map Apple                 63 @ 1      
   3:      Apple_Driver43*Macintosh             32 @ 64     
   4:     Apple_UNIX_SVR2 Swap              262140 @ 96      (128.0M)
   5:     Apple_UNIX_SVR2 Root file system 1462440 @ 262236  (714.1M)
   6:          Apple_Free Extra                 29 @ 1724676
  
   i.e.  MacOS HFS partition = /dev/sdb1
         MkLinux Root =        /dev/sdb5
         
1. Download the kernel (Mach_Kernel.gz), Linux (vmlinux.gz) and System Map 
   (System.map.gz), using binary transfer from: 

 ftp://globegate.utm.edu/pub/MkLinux/kernels/development/
   or
 ftp://ftp.mklinux.apple.com/pub/contrib/kernels/development/

2. If they are not automatically unzipped, drop each on Stuffit Expander.

3. Rename Mach_Kernel to Mach Kernel and put it in  
   macos_boot_disk:System Folder:Extensions:

4. Put System.map and vmlinux in 
   mklinux_macos_partition:mach_servers

5. Copy bootstrap.conf and default_pager 
     from the MkLinux DR3 CD-ROM in the mach_servers folder  
     to mklinux_macos_partition:mach_servers
  
6. At this point mklinux_macos_partition:mach_servers 
   should have the followingf four files:
     System.map           - from Gatewood ftp site
     vmlinux              - from Gatewood ftp site
     bootstrap.conf       - from MkLinux DR3 CD mach_servers folder
     default_pager        - from MkLinux DR3 CD mach_servers folder

7. Using BBEdit Light, so as to preserve UNIX line endings, edit 
   bootstrap.conf to read:  

  -w default_pager /dev/boot_device/mach_servers/default_pager
  -k -S 524288000 startup /dev/boot_device/mach_servers/vmlinux -c "root=/dev/sdb5"

The only changes are to the end of the second line. 
  - vmlinux rather than vmlinux+installer
  - root="/dev/sdb5"  /dev/sdb5 is my MkLinux root partition. It will be different 
    on your system.

8. Using any text editor (e.g. SimpleText, BBEdit Light) edit 
   boot_volume:System Folder:Preferences:lilo.conf to read:

     rootdev=/dev/sdb1      # HFS partition


(Make sure there are a couple of blank lines at the end of the file.)
 /dev/sdb1 is my HFS partition. It will be different on your system.

Final note: 
According to Chris Garrigues <cwg-dated-910255829a86aa80@DeepEddy.Com>,
"You can mix and match vmlinux versions with Mach Kernel versions if
one of them causes you a problem."

Sources:
BBedit Lite http://web.barebones.com/free/free.html

Steve Knouse
November 29, 1998