>It autoconfigs just fine, but hangs at the
>"changing root device to sd0a"
>message.
>
>What is the most likely thing that I have done wrong?

I've seen this happen when all the right devices aren't created on the root
partition.  Since you say you can boot off of a floppy, do so and check to
make sure everything in /dev exists.  You might consider running "MAKEDEV all"
to be sure everything is created.

--Ken