I really like your fork analogy.. it's amazing..
But yeah, if you have more than one kernel, both kernels will reside in your /boot dir, you won't/can't have 2 (well, you can, but it's really no a good idea...) you won't have two / or two different /home/user directories either...
The kernel is the core of the operating system, which differs from your GUI (graphical user interface).
Unlike windows/osx, *nix systems use a Monolithic kernel (this means that, basically, everything is run through the kernel or modules in the kernel). Windows systems use a Microkernel, which is much smaller, and everything has to be loaded on top of it.
Check out this site:
http://en.wikipedia.org/wiki/Kernel_...ter_science%29
Basically, you need to recomiple the kernel in Linux because if something isn't in it (support for a device/protocal/or whatever) you can add it, or take something out thats in there that you don't need. You can speed up or slow down your system depending on how much extra crap you have compiled into your kernel.
That's why you need to recompile, and even though you don't have to, I would recommend trying it once, just to play around. I always keep my old kernels, becuase if my newly recompiled one breaks cause of something I did to it, I can always boot into the older one. Cause, like someone else said, you can have as many kernels compiled as you want (I have about 3 on my system.. 2.4, 2.6, and my experimental 2.6.10 where I test settings and whatnot and try to tweak my system..... it keeps me from getting bored and destorying my computer in other ways) but you can only use one kernel at a time...
to delete one, just delete the image from your /boot directory, the source from /usr/src/ and the libs (from I forogt where)...
Also, you must have the kernel source installed on your system to recompile/compile.. You can use Mandrake's, which should be on your CD's, or you can download the offical non distro specific Vanilla Kernel, from
www.kernel.org (that's the direct from source Linux Kernel from Linus' team)
Happy compiling!