VPN Ping Strangeness

I can successfully connect to my VPN server which sits behind Linksys
WRT54G router. I can successfully ping the server itself and some other
machines
on the network (domain controller/DNS server) although they report some lost
packets.
However another machine on the network (problempc.domain.com) only
respondons to the first ping
all the consequtive pings are Timed Out. I can't connect to it with RDC
either.
I use cable connection for VPN so that's not the issue. All the firewalls
are disabled
on the router and individual Pcs. The problem machine is running winxp sp2.

thank you very much for all the help