I checked the /etc/src/ directory and I don't have any of the directories you mentioned. I mean there was no redhat directory there.
I created /usr/src/redhat/SOURCES directory and successfully installed kernel-2.4.20-19.9.src.rpm. Then I extracted the source
> tar xvzf NVIDIA_nforce-1.0-0261.tar.gz.
> cd nforce/nvnet
> make clean
The last command gave the output:
cc -c -Wall -DLINUX -DMODULE -DEXPORT_SYMTAB -D__KERNEL__ -O -Wstrict-prototypes -DCONFIG_PM -fno-strict-aliasing -mpreferred-stack-boundary=2 -march=i686 -malign-functions=4 -DMODULE -I/lib/modules/2.4.20-19.9/build/include nvnet.c
make: cc: Command not found
make: *** [nvnet.o] Error 127