For those of you wondering if this is possible I have managed to get this working. Here's what you need to do:
1) On your RIS server create the following folder structure: SetupEnglishImagesPXELinuxi386templatespxelinux.cfg (pxelinux.cfg is a fodler)
2) Download the latest version of syslinux from:
[/url]http://www.kernel.org/pub/linux/utils/boot/syslinux/[url]
3) From the ESX 3 (this works with 2.5.x as well) CD (imagespxeboot) copy the following files to SetupEnglishImagesPXELinuxi386templates
vmlinuz
initrd.img
ntoe: you MAY want to rename these files IF you plan on have multiple versions of ESX builds available.
4) from the file you downloaded in step 2, copy the pxelinux.0 to the templates folder.
5) create a file called pxelinux.sif file in the template folder with the following contents:
[OSChooser]
Description = "Linux"
Help = "This option runs a Linux installer."
LaunchFile = "SetupEnglishImagesPXELinuxi386templatespxelinux.0"
ImageType = Flat
Version="1.01"
6) in the SetupEnglishImagesPXELinuxi386templatespxelinux.cfg folder create a file called 'default' (no extension) with the following info.
DEFAULT esx
prompt 1
display boot.msg
timeout 1000
label esx
kernel vmlinuz
append initrd=initrd.img
This is the info you've placed in the syslinux.cfg file. Since no files are stored on the RIS server, you'll will need to build ESX via http/ftp or NFS. I'm using FTP via IIS 6.0 and it works quite well.
If you want a boot message, then copy the boot.msg file to SetupEnglishImagesPXELinuxi386templates
Once you do the PXE boot you should see a "server build" called Linux and when you select it, it will eventually present you witht he "boot:" option where you can select the build that you want.
Enjoy!
disclaimer: I didn't invent this method, I actually found it looking for info on parameters used in ks.cfg/syslinux.cfg.