No, it will not, nor will you be able to activate it, as it can only be activated on a Dell machine with the proper license (which license belongs to the computer).  To run Vista virtually legally on your Toshiba, you must purchase a Retail copy of Vista.
I have Vista on my Dell desktop. My notebook is a Toshiba running Windows 7. Unfortunately, I have a very important program that will not run properly on Windows 7 and there is no application upgrade available to make it run on Windows 7. I want to install a virtual machine on my Toshiba and install Vista on it. Will the disk containing Vista for Dell that came pre-installed on my XPS 420 work if I try to install it on the virtual machine. Thanks, in advance, for any help.
Install Vista for Dell on Toshiba w/virtual machine