Do you now have the hosts trying to traverse the PIX with the internal interface of the PIX as their default route?

Yes I do. At least the host that is now behind the PIX for test purposes. I'm using the .192 segment specifically for trying to get the firewall configuration knocked out. The rest of my network use the router's IP at .129 as it always has, since they're all on the same network as the router (and now, the outside interface on the PIX).

I'll take into consideration all the advice I'm getting about firewall makes and models the next time I'm making the purchasing decision, but so far that's never been my role.