Is there a way to do virtual interfaces (having the kernel accept packets
   for multiple IP addrs on the same network interface) under NetBSD?  I've
   got a file describing how to add vifs by John Ionnidis, and was wondering
   if this functionality had already been integrated to NetBSD.

look at ifconfig's alias command.

someone needs to fix ifconfig(8) to print the aliases as well..

.mrg.