I already described the basic interface of VirtualBox 4.0 Command line here:
You can also stumble upon a problem while installing Windows XP with SATA controller VDI drive. There are two types of hardware controllers in "system" tab (VM settings) - ICH9 and PIIX3. I didn't manage to install WinXP on ICH9 yet but it is possible to install XP with SATA support.
All you need to do is add a "Floppy Controller" in storage tab and mount this image:
The when you install Windows XP press F6 during boot time and select:
"s" - load additional drivers
"Intel(R) 82801HEM/HBM SATA AHCI Controller (Mobile ICH8M-E/M)"
then continue with the setup process as usual.