well, i use geexbox live-cd, using "hd-install" (or "install-hd", i don't remember well :-)) choosing the usb-key drive as HD on which install it.
Then, to add the many distros, i use live cds (dsl, slack & systemrescuecd).
For example, damn small linux live cd use syslinux to boot.
So, i look at kernel and initrd listed in it's /boot/isolinux/isolinux.cfg (the syslinux configuration file in the live cdrom, in this case from the old version i used):
DEFAULT linux24
APPEND ramdisk_size=100000 init=/etc/init lang=us apm=power-off vga=791 initrd=minirt24.gz nomce noapic quiet BOOT_IMAGE=knoppix
TIMEOUT 300
..and modify grub menu.lst (the grub installed by geexbox, in the usb-key drive) in this way:
....
title DamnSmallLinux (GNU/Debian based)
root (hd0,0)
kernel /dsl/linux24 ramdisk_size=100000 init=/etc/init lang=it apm=power-off vga=791
initrd /dsl/minirt24.gz nomce noapic quiet frugal restore=sda1 BOOT_IMAGE=knoppix
boot
.....
So i "convert" syslinux boot string into a grub stanza.
I don't install DSL in any way, i boot that in LIVE mode from usb-key drive.
And so on for the other distributions.
So i think that there's no problem with the debian net-install (for example: looking at debian-40r1-i386-netinst.iso) - there's a folder called "isolinux" with file "isolinux.cfg":
...
LABEL install
kernel /install.386/vmlinuz
append vga=normal initrd=/install.386/initrd.gz --
LABEL linux
kernel /install.386/vmlinuz
append vga=normal initrd=/install.386/initrd.gz --
LABEL installgui
kernel /install.386/vmlinuz
append video=vesa:ywrap,mtrr vga=788 initrd=/install.386/gtk/initrd.gz --
LABEL expert
kernel /install.386/vmlinuz
append priority=low vga=normal initrd=/install.386/initrd.gz --
LABEL expertgui
kernel /install.386/vmlinuz
append priority=low video=vesa:ywrap,mtrr vga=788 initrd=/install.386/gtk/initrd.gz --
...
where you can find out the kernel, the initrd and many boot options.
You had to copy all the contents of the live cd (excluded autorun.*, readme.* etc etc, if you want) and edit grub menu.lst.
Instead of grub you can use syslinux (i don't remember why i choose to use grub, at the end).
But the way is about the same: you must put in one file (grub way: menu.lst or syslinux way: syslinux.cfg ) the boot string for all the kernel you have in the usb-key drive.
Hope it helps you a little more...
Bye!