VPN hides some systems

Hi,
When I am connected to my work via vpn, I cannot see some systems,
others I get one reply from a ping, and others I can see and control
without issue. When I am on site, everything shows up on the network
so it's just through vpn.

I have a 2000 adv server PDC that is the vpn server and dns server. I
have a 2003 server (that will house isa soon) that is running dhcp.
On vpn I cannot ping the dhcp server but when I set it up as a dhcp
relay Routing and Remote Access I get ip addresses for vpn.

I just set up the PDC and started setting up the isa but I uninstalled
it so that I could troubleshoot. Everything was in a workgroup and
worked perfectly before I started this mess.

Thanks for the help
P