Help: Mandrake 10.1 routing problem?

I have an old RH7 box which I just repaved with Mandrake 10.1. It sits
on my home network and must access the internet via a W2K box (which is
configured for Internet-Connection-Sharing with two ethernet cards in
it: one for the cablemodem and one for the local network). I've
configured the linux card to obtain its IP address from the W2K machine
via DHCP, and this appears to work (the lights flash, it only takes a
couple of seconds, and it gets the address 192.168.0.75).

However, neither machine can ping each other. The linux ping output is
(copying from one monitor to another, beware of typos):

PING 192.168.0.1 (192.168.0.1) 56(84) bytes of data.
From 192.168.0.75 icmp_seq=1 Destination Host Unreachable
From 192.168.0.75 icmp_seq=1 Destination Host Unreachable
From 192.168.0.75 icmp_seq=1 Destination Host Unreachable
From 192.168.0.75 icmp_seq=1 Destination Host Unreachable
From 192.168.0.75 icmp_seq=1 Destination Host Unreachable
From 192.168.0.75 icmp_seq=1 Destination Host Unreachable
ping: sendmsg: Operation not permitted
From 192.168.0.75 icmp_seq=1 Destination Host Unreachable
ping: sendmsg: Operation not permitted
From 192.168.0.75 icmp_seq=1 Destination Host Unreachable
ping: sendmsg: Operation not permitted

etc...


"route -n" gives:

Destination Gateway Genmask Flags Metric Ref Use IFace
192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
0.0.0.0 192.168.0.1 0.0.0 UG 0 0 0 eth0

(I'm a bit concerned about the lack of loopback device, but I can ping
localhost OK, so maybe that's nothing to worry about.)


I also tried "ping -b 192.168.0.0" (just to see what happened) and got:
ping: sendmsg: Operation not permitted


The error messages point to a routing problem, but I can't see what's
wrong. I'm fairly sure there are no hardware problems, as before the
upgrade the network functioned well (BTW, the NIC cards are all
rtl8139(too), I believe). Are there some other tests to try, or output I
can examine, to determine what's wrong?


Thanks,
Alistair.