Sun Open Firmware - insiders?

I have a question regarding Sun OpenFirmware that's been bugging me for some time now. I'm still struggling for a setup that allows a Sun to netboot off a Windows 9x PC (just get a bootstrap, no fancy NFS exports required). I'm making do with SuSE Linux 7.0 dual-boot right now, but that's not it. What I'm imagining here is to have a look at the code that is responsible for the netbooting operation of the Sun. Why does it have to obtain the machine's IP, that of the tftp server and what else via rarp? I'm by no means a Sun expert yet, but as I've understood it, you can define your own FCode commands and store them in NVRAM, so one could modify the boot code to use parameters stored in environment variables, either if a flag "use-stored-IP?" is set or as a fallback if there's no rarp server around.