How do I provide the 'stage2=' parm for RHEL 6.1 PXE boot?

Hi

I would like to specify the stage2 parameter to a RHEL 6.1 PXE boot, I have added the parameter to the 'append' line in the isolinux.cfg/default
but during the pxe boot sequence I get the INFO that stage2= has not been specified.
I have tried using 'stage2=' and 'inst.stage2=' neither works.
(stage2=nfs:IP_ADDR:/PATH_TO_IMAGE_STRUCTURE.

Any ideas, or hints to where this might be documented?

Thanks

Henrik