I'm a long time Backtrack user, but new in the forums.

BT4 beta ships with a new 2.6.28+ kernel, which supports the paravirtualized Virtio drivers for network, block device (harddisk), PCI passthrough and memory (all supported since 2.6.25). These drivers makes it possible to run BT at very close to native performance in a Linux-based virtual environment with for example the KVM (kernel virtual machine) hypervisor. KVM is today the default virtualization solution on both Fedora and Ubuntu, and many other Linux distributions.

However, these modules are not enabled by default in BT4 beta.

BT already supports Vmware, so why not also support the leading open source virtualization solution? All you need to do, is to enable four modules to be compiled into the kernel. The latest versions of Fedora and Ubuntu also ships with these modules enabled by default, to allow an optimal installation in a virtual environment.

Information about the needed modules:
linux-kvm . org / page / Virtio
(sorry, I'm not allowed to post links yet)

A more general description on Virtio taken from the libvirtd wiki:
So-called "full virtualization" is a nice feature because it allows you to run any operating system virtualized. However, it's slow because the hypervisor has to emulate actual physical devices such as RTL8139 network cards . This emulation is both complicated and inefficient.

Virtio is a Linux standard for network and disk device drivers where just the guest's device driver "knows" it is running in a virtual environment, and cooperates with the hypervisor. This enables guests to get high performance network and disk operations, and gives most of the performance benefits of paravirtualization.

Note that virtio is different, but architecturally similar to, Xen paravirtualized device drivers (such as the ones that you can install in a Windows guest to make it go faster under Xen). Also similar is VMWare's Guest Tools.

I really hope that it would be possible to include these modules in the BT4 final version Looking forward to your reply...

Best Regards