Network question: Cross network browsing

[Joel Hammer]

I have a main network and a subnetwork, with a router for the latter.
>From the main network, I can ping a linux box and a XP home edition
box on the subnet, but I cannot ping a second windows box, an XP Pro,
on the subnet. I can ping this problem box from within the same subnet.
Is this an XP Pro thing or should I look into some sort of firewall on
the XP Pro box?

Thanks,

Joel