(this guide was written by Brian Stuart)
(taken from this no-longer-online page)

How to Build a Native Inferno Kernel for the PC
When we're done, we'll have a floppy disk image. This image can be written to a 
floppy that a PC can boot from. It can also be used as the El Torito boot file 
for a bootable CDROM. These images (floppy or CDROM) can also be run in any 
number of PC emulators. I've done a lot of my testing running them in qemu.

Set Inferno Configuration

Set the appropriate values in mkconfig in the Inferno root directory. Pay 
particular attention to the variables ROOT, SYSHOST, and OBJTYPE.

Building the Tool Chain
If you're working in Windows, you already have the toolchain in place in 
C:\Inferno\Nt\386\bin. For other host OSs (Linux, FreeBSD, Plan9), a 
"mk install" issued at a host OS prompt in the Inferno root directory. Be sure 
your PATH environment variable includes your Inferno binaries directory.

Configure the Native Kernel and Install Boostrapping Code
Don't worry, we're not installing the Inferno bootstrapping code to your host 
machine. We're just building it and putting it in a standard place so we can use
it later.

1. In os/boot/pc in the Inferno tree, issue the command 
   "mk pbs.install 9load.install" at a host OS prompt.
2. Edit os/pc/pc to set up the kernel configuration. A simple/minimal set of 
   changes to get something that you can see working is:
  1. Change wminit to shell in the init section.
  2. Set the consoleprint variable in the code section to 1.
  3. Add the files /dis/lib/arg.dis and /dis/lib/filepat.dis to the root section.
3. Create a file in os/pc called plan9.ini. If you're going to boot directly 
   from the floppy, it should include the line: "bootfile=fd0!ipc.gz". If you're
   going to build a bootable CD, the line should be "bootfile=sdD0!cdboot!ipc.gz".
   This assumes your CD is the master drive on the second IDE controller, which 
   is probably the most common configuration.

Build the Floppy Image
1. Issue the "mk" command in os/pc at a host OS prompt.
2. Issue the "gzip ipc" command in os/pc at an Inferno shell prompt.
3. Issue the following command in os/pc at an Inferno shell prompt:
   disk/format -b /Inferno/386/pbs -df disk /Inferno/386/9load plan9.ini ipc.gz
The result will be a file called "disk" that can be written raw to a floppy or 
used to create a bootable CDROM.