To setup KNOPPIX to boot from RIS I did the following:
1. Create the following folder structure on my RIS server: <drive>:\RemoteInstall\Setup\English\Tools\Knoppix \i386\templates (I created the Knoppix, i386, and templates folders).
2. In the templates folder create a text file that has a .SIF extension. The file name doesn't really matter but I called mine pxelinux.sif.
3. The pxelinux.sif file (or whatever you choose to call yours) should contain the following (you can customize the Description and Help sections to your own preference if desired):

[OSChooser]
Description = "Boot Knoppix Live Linux Environment"
Help = "This option boots into a live Linux environment with a full shell, internet browser, diagnostics tools, applications, etc."
LaunchFile = "Setup\English\Tools\Knoppix\i386\templates\pxelin ux.0"
ImageType = Flat
Version="1.01"

4. In the <drive>:\RemoteInstall\Setup\English\Tools\Knoppix \i386\templates folder create another folder called "pxelinux.cfg" (including the dot).
5. In the <drive>:\RemoteInstall\Setup\English\Tools\Knoppix \i386\templates\pxelinux.cfg folder create a text file called "default" (with no file extension).
6. The troubles I am having are likely related to the following contents of my particular "default" file so the following may not necessarily be correct:

default knoppix
prompt 0
timeout 30
LABEL knoppix
KERNEL linux
APPEND netboot=nfs nfsroot=192.168.0.7:/KNOPPIX -- nodhcp lang=en ramdisk_size=100000 init=/etc/init apm=power-off nomce vga=791 initrd=miniroot.gz quiet BOOT_IMAGE=KNOPPIX

7. In the <drive>:\RemoteInstall\Setup\English\Tools\Knoppix \i386\templates folder copy miniroot.gz, pxelinux.0, linux, and pretty much any other file from the root of the Knoppix CD, including the 700MB "KNOPPIX" file. You may have to mess around with file paths in the "default" file and pxelinux.cfg a bit as well as change locations of the files you copied to subfolders, etc. I actually have the CD contents copied into *every* folder and subfolder beneath my <drive>:\RemoteInstall\Setup\English\Tools\Knoppix \i386\templates folder structure for troubleshooting purposes.
8. Restart Remote Installation Services (or Windows Deployment Services (WDS) Server for Windows Server 2003 SP2) and Trivial FTP Daemon for the changes you just made to take effect.

Please let me know if you get further than I did. I would *really* like to get this working.