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I have two VirtualBox machines on one computer both with Windows XP. How to set network adapter at one and the second machine to be networked ? Tnx

You haven't read the Forum Posting Guide. Please do so and follow it. Right now, you don't give enough information to answer the question.

Yes i read user manual but nothing... I used VMware Workstation but I've moved on VirtualBox is a little different. I know there are few network modes. NAT, Bridget, Internal and Host-only but I fail to set network. My problem is the following...
I have one PC where it is installed VirtualBox. In VirtualBox i have two machines WindowsXP1 and WindowsXP2. All i want is the set the network adapter of WindowsXP1 and WindowsXP2 that could to communicate when start WindowsXP1 and WindowsXP2 machine. Do not communicate with PC where they VirtualBox are installed. Probably is easy but I fail...

You just described the "Internal networking" feature.

I have already tried with Internal Network and default name intnet. WindowsXP1 machine have ip adress 192.168.1.1 and WindowsXP2 machine have ip adress 192.168.1.2. When i ping 192.168.1.2 from WindowsXP1 or 192.168.1.1 from WindowsXP2 i get the message "Request Timed Out". I try with VBoxManage dhcpserver but the message is the same. What's the problem in this ?

XP firewall.