The netmount init script is run before the nfs init script. This will cause the boot process to hang if nfs mounts in fstab are set to mount at boot. Temporary fix is set nfs mounts to not mount a boot. then manual mount them at a shell prompt. This is a pain for me in that I have quite a few nfs mounts that I normaly mount at boot. This is for Version 1.1a BTW. Sugested solution have the netmount init script check to see if portmap is running. if not start it. But only do this if nfs mounts are to be mounted. You may also look into implementing a time out in case the user gets the fstab wrong simular to what mandrake/redhat do.
Look at the netmount initscript. It already will run portmap if it is *ADDED* to the "default" runlevel. The logical reasoing is that if a user use nfs mounts, he will merge portmap, and then add it to the default runlevel: # rc-update add portmap default Check if this solves your problem.