networking problem between vista and xp machines

Is this the right group? Please let me know if I should be posting

My friend has four machines:
- deskop (xp sp2)
- laptop1 (xp sp2)
- laptop2 (vista home)
- posTerm (xp sp2)

Booting normally, I can issue "ping laptop2" on the xp machines. they
translate that to the correct IP address for laptop2, but all packets
are lost. Windows Explorer can map a drive to \\laptop2\c$\, but I
cannot browse any of the machines in the workgroup. Laptop2 resolves
IP addresses correctly, but cannot ping nor map to the xp machines.

Booting to Safe Mode With Networking, I ping commands resolve the
correct IP address but only pings between xp machines work -- pinging
the vista box fails, pinging FROM the vista box fails. When in Safe
Mode With Networking, going through Windows Explorer I am able to
browse the other machines in the workgroup and can see the C or C$

I have reset the router and that works (also resolved an odd DNS
setting while doing so). The router is DHCP host, appears to be
working fine. All machines can connect to the internet without
issue. All machines have Hamachi and VNC installed -- I can dial in
remotely without issue. All machines can see MY machine across the
Hamachi VPN.

Where should I be looking?