I have FreeBSD 4.x and "rndc-confgen -a" just sits there.

/dev/random is not configured. Use rndcontrol(8) to tell the kernel to use certain interrupts as a source of random events. You can make this permanent by setting rand_irqs in /etc/rc.conf.

rand_irqs="3 14 15"

See also: What does "no source of entropy found" or "could not open entropy source foo" mean?