Bashing my head on a wall with this

I have managed to get ESXi to boot and install fine using these tutorials:

https://help.ubuntu.com/community/PXEInstallServer
https://help.ubuntu.com/community/PXEInstallMultiDistro

Everything is perfect for ESXi 4/5 & Ubuntu

I cannot however get Freenas(or XP for that matter) to boot. I don't know what to point the pxelinux.cfg/default file to.
MEMDISK doesn't work either, as it asks for a ramdisk (when trying to boot straight from an iso image).

Does anyone know what to point it to?
For example I can boot esxi by adding something like this(with a kickstart of course):

kernel esxi/mboot.c32
append esxi/vmkboot.gz ks=http://192.168.111.101/ks.cfg --- esxi/vmkernel.gz --- esxi/sys.vgz --- esxi/cim.vgz --- esxi/ienviron.vgz --- esxi/install.vgz (copied from: http://pookey.co.uk/wordpress/archives/235-installing-vmware-esxi-via-pxe)


Any help would be fantastic