This is how I configured NFS root on my pandaboard. There is also complete boot partition in [1]
1) Install grubby, u-boot and dracut-network from my repo [2]
2) Install kernel-omap. This kernel have path that allow you to set mac address for smsc95xx with smsc95xx.macaddr kernel boot argument.
3) Change KERNEL_ARG in /etc/sysconfig/uboot for dracut network boot [3]
KERNEL_ARGS="ro vram=32M root=dhcp fixrtc console=ttyO2,115200 mem=460M@0x80000000 mem=512M@0xA0000000 omapdss.def_disp=dvi smsc95xx.macaddr=5A:3E:83:2D:BA:41 selinux=0"
4) Add option "root-path=SERVER:PATH" to dhcp server host pandaboard1 { hardware ethernet 5a:3e:83:2d:ba:41; fixed-address 10.21.38.31; option root-path "10.21.38.4:/nfs/pandaboard1-fc15"; }
5) Run "flash-kernel --update-bootscript 2.6.38.8-36.06.fc15.armv7hl.omap"
[1] http://zpericic.fedorapeople.org/boot/