Use your current WINS or dynamic DNS server for name resolution. On each PPTP client, manually enter either the WINS or DNS server under advanced networking properties of the PPTP connection.
NT/SME (samba) run WINS. If you are running AD, you have dynamic DNS. If using DDNS, make sure each PPTP client (2000 & XP only) are set to register with the DNS server.
If your LAN and PPTP clients use the same name resolution server, all should be able to communicate by host name.
ryan