Requirement : VirtualBox
In this guide :
Host = Windows XP(32bit OS)
Client = SmoothWall(32bit OS)
INSTALLING SMOOTHWALL AS CLIENT
I'm using static IP address for my network connection.
HOST
1. Go to Control Panel->Network Connections
2. Bridge your Local Area Connection and VirtualBox Host-Only Network adapter by highlighting both adapters, right click on it and click "Bridge Connections".
After successfully bridge your network adapters

3. Set your static IP address for your Network Bridge by right-click Network Bridge->Properties->Internet Protocol(TCP/IP)
4. Open Sun VirtualBox->New

-Click Next

-Click Next

-256MB Memory Needed for SmoothWall
-Click Next

-Click Next

-Click Next

-Select Fixed-size expanding storage
-Click Next

-I'm going to use 10GB of HDD space for my SmoothWall Virtual Machine .
-Click Next then click Finish
Open your Sun VirtualBox control panel.

-Highlight "SmoothWall" and click "Settings"
-Go to Network

-Then

-As we can see, we're going to use 2 virtual Network Adapters for our SmoothWall because SmoothWall need at least 2 Network Cards.
-Go to CD/DVD-ROM tab

-Mount your SmoothWall installation CD or ISO.
-If you don't have one, you can download from here(32bit).
-And click OK.
-Go back to VirtualBox control panel

-Click Start
-Follow this tutorial for the SmoothWall installation procedure.
SMOOTHWALL INSTALLATION PROCEDURE