When you want to do a P2V ( physical to virtual ) migration Microsoft expect you to have a or build a management environment for it. This is great because you can monitor the environment before you turn it in to a virtual one.This is when time is on your site. In the picture below you see the Microsoft possibilities for migrating to a virtual environment
The picture comes form the Converting Physical Computers to Virtual Machines in VMM document. With give you great information on how to P2V V2V etc.
With System Center Virtual Machine Manager (VMM) you can do the migration to virtualization. But is some cases this will not work. Like when it is not in the same domain (and you may not connect to it) or when it is in a other datacenter like it was in my case and the line well there was a line but not something you would like to mention.
There is a tool from Microsoft (actually from sysinternal) they makes it possible to do a live P2V action of a server with out VMM. It is a small tool called: Disk2vhd. at the moment it is al version 1.5. this is the version I worked with. I did a couple of p2v and found out it was working great for system disks, but not for ISCSI attached disk this always went wrong. But that where the data disk so there are other solutions for that. I think it is a nice and handy tool but remember Microsoft will not support you with this tool. And it is only for Microsoft operating systems. Linux P2V is not supported in any way bij Microsoft at the moment there is a way of getting it don but you must partly rebuild the Linux after the P2V action to get it working.