Unfortunately the images from the site have activation issues because they see it as being installed on new hardware, someone from MS posted on the VirtualBox forum suggesting an email to see if the demand was high enough and I guess it hasn't reached that point yet. http://forums.virtualbox.org/viewtopic.php?f=2&t=21712&#...
For my own system I used MSDN to get working installs of XP on my Mac in VirtualBox.
You also need to convert the VHD to VDI. I've done this on Mac using Q (http://www.kju-app.org/) and these simple commands.
/Applications/Q.app/Contents/MacOS/qemu-img convert -O raw -f vpc "input.vhd" temp.bin
For my own system I used MSDN to get working installs of XP on my Mac in VirtualBox.
You also need to convert the VHD to VDI. I've done this on Mac using Q (http://www.kju-app.org/) and these simple commands.
/Applications/Q.app/Contents/MacOS/qemu-img convert -O raw -f vpc "input.vhd" temp.bin
VBoxManage convertdd temp.bin "output.vdi"