How to boot from file without CD?

[Peter Neilson]

I've got 6.2 (zoot) already running on a Dell Gxi, which is a
desktop with a BIOS that has the silly notion that no one
would ever want to boot from CDROM.  There is no way to boot
this unfortunate machine from CDROM.  Don't bother going there.

How did I get zoot running on the GXi?  I had it running on
another machine that croaked, took /dev/hda from it and bolted
it into the GXi as /dev/hda, moving the GXi's hda to hdb.

The plan is to install FC3 onto /dev/hdb and then swap hdb
with hda again, leaving a machine that'll boot right into FC3,
and all my user files from zoot days will be right there on hdb.

So right now I've got the contents of the four CDs
downloaded into files on the GXi, and I can read them fine
because I've got them mounted by using commands like this:
mount -o loop -t iso9660 FC3-i386-disc4.iso d4

Now what?  I've seen some stuff about images/boot.iso and
something about grub.

But I don't know ANYTHING about grub.  Maybe I've been
looking in the wrong places.  zoot does not use grub, as
far as I know, just comes up through lilo boot.

I'll bet it's all probably easier than I've imagined.
Any suggestions?  Maybe a list of explicit steps?  I'd like
some explicit steps, not just vague hand waving.

Thanxx.