Dialing to a LAN and ping internal IP in XP SP2

[ServerHead]

Consider a LAN wof 2 PCs each running XP SP2 with Firewall up and ICMP incoming echo allowed with following IP setting:
PC1 IP: 192.168.1.1
PC2 IP: 192.168.1.2 GW: 192.168.1.1

Now consider that PC1 has a modem with Incoming Connections configured with settings:
Allow callers to access my local area network - ON
IP Range: 200.200.200.1 to 200.200.200.10

Now, PC3 with IP 192.168.2.1 dials to PC1 and gets an IP for Dial-up interface as 200.200.200.2 and PC1 acquires 200.200.200.1

After connect PC3 can ping 200.200.200.1 but cannot ping 192.168.1.1 of PC1 or 192.168.1.2 of PC2. Also, PC1 can ping 200.200.200.2 without any problem.

Internal IPs could be pinged in Win2K without any problem and also works in XP SP2 but only with firewall OFF.

How to make it work without switching off firewall in XP SP2?