Keep in mind that migrating or converting a PC generally has two issues:
1) Unless you purchased that OS at retail, it's likely an OEM license which is tied to the physical hardware (and can't be virtualized).
2) It will result in a bloated, unstable, buggy virtual machine.
Given 1 (i.e. that you have to have an installable license anyway), why not avoid 2 and create a new clean VM from scratch?