virtualbox.org

I installed VirtualBox 3.0.2 on my laptop (Windows XP S2 -- PC1) and installed 2 other OSes inside the VirtualBox: WinXp S2 (PC2) and Ubuntu 9.04 (Server version -- PC3). Both of them can access to Internet normally and have same IP address: 10.0.2.15 (The IP address of PC1 is "192.168.1.13").

Now I want to setup the PC3 as a Domain Controller and PC2 is a client. But I don't know how to setup a LAN network between PC2 and PC3.

Is there any solution for this issue?

Use Bridge networking.

I tried and here are new IP addresses:
PC1: 192.168.1.13
PC2: 192.168.1.217
PC3: 192.168.1.218

When I ping PC3 from PC1 and PC2, I receive the reply packets. But when I ping from PC1 and PC3 to PC2, no packets received.

Firewall ?

I installed a new virtual XP machine and it works.

I don't think that is a problem of firewall but it's not a matter now

Instead of bridging, you could have used Internal Networking. It's made for this kind of thing. Only the VMs can communicate with each other, the Host and rest of the physical network has no idea about them.