adding another XP machine to LAN

I have a network with an XP pro and two 98 machines and
the newtwork works great. I have now added another XP
pro machine and that is where my problems have started.

Symptoms: When viewing workgroups on any machine (98 or
XP ) they are visible but as soon as either XP machine is
double clicked to access the other XP machine the
following errors occur: XXX not accessible - see
administrator followed by one of the following:
(The server is not started; MSHOME not accessible;or
Network path is not found)

The 98 machines can access either XP machine with no
problem and the old XP machine can access the 98 machines
but niether XP machine can access each other.

The network is setup through Dlink 704 router and all
macines have the ISP's in auto.

Does anyone have any ideas?

Thanks

Richard