VirtualBox NAT Port Forwarding Settings(Windows XP)

Applies to VirtualBox 2.0
Use VBoxManager.exe (In VirtualBox installation directory).

Type in command line:

VBoxManager.exe setextradata "GuestName" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/Protocol" TCP
VBoxManager.exe setextradata "GuestName" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/GuestPort" 22
VBoxManager.exe setextradata "GuestName" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/HostPort" 29876

"GuestName" is name of virtual machine.
"ssh"        is just a name for this port forwarding, can be anything

This will add the following lines in the virtual machine's .xml file:

<ExtraDataItem name="VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/Protocol" value="TCP"/>
<ExtraDataItem name="VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/GuestPort" value="22"/>
<ExtraDataItem name="VBoxInternal/Devices/pcnet/0/LUN#0/Config/ssh/HostPort" value="29876"/>

To add another port forwarding, use another name and port sets, e.g.:
VBoxManager.exe setextradata "GuestName" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/web/Protocol" TCP
VBoxManager.exe setextradata "GuestName" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/web/GuestPort" 80
VBoxManager.exe setextradata "GuestName" "VBoxInternal/Devices/pcnet/0/LUN#0/Config/web/HostPort" 8080

To set a global port forwarding, use "Global" instead of "GuestName", and the change is made in VirtualBox's global settings .xml,
usually it's at C:/Documents and Settings/<Profile Name>/.VirtualBox/VirtualBox.xml

All settings above require to close virtual machines and restart VirtualBox.