VirtualBox on existent Vista/Ubuntu dual boot

Is it possible to use Virtualbox to boot from that old real drive instead of from an image?

Yes. VirtualBox has support for using a raw host hard disk from a guest since version 1.4. As of version 2.2.0, it is still listed as an experimental feature. It is described in section 9.10 of the user manual for VirtualBox 2.2.0.

There are some instructions for running a WindowsXP guest using a raw host hard disk on a linux host:

• http://mesbalivernes.blogspot.com/2008/01/virtual-box-booting-from-existing.html
• http://ubuntuforums.org/showthread.php?t=769883

If so, what are the implications for drivers, etc, since the "new" running OS will be using VirtualBox's virtual hardware and not the original hardware on which XP thinks it was installed.

The second link above describes some steps to prepare your XP system prior to booting under VirtualBox.

There are several ways you can approach this:

• Don't use a NAT adapter. I realize this may not be possible/desirable, but if you can select "Bridged" adapter and get an IP from that same subnet, all these problems (both gust->host and host->guest) go away.

• Use two virtual adapters, the regular NAT one for internet access, and a second "loopback" adapter in bridged mode on your own private subnet. The loopback will be used for communication between the host and guest(s), while the NAT adapter will handle the traffic outside of the host.

• There are a number of tricks to do port forwarding to the hosts, as well as open up guests to see the host. By default, I believe, both of these are blocked as to provide a better sandbox. There are plenty of questions here on Server Fault (tagged with VirtualBox) that talk about punching holes as described.