"A physical server needs drivers to talk to it's hardware. A virtualized server, in essence, does the same thing. VMware presents new hardware to allow the virtual machine to talk to it's hypervisor. Think of the driver issue in a P2V migration like removing a video card and installing a new one. The drivers and hidden hardware are still there just in case you feel like popping the video card back in. A P2V will still have all of the old hardware in the virtual machine. Don't forget about services that physical servers used, namely HP server management services."
Ultimate-P2V (fix-vmscsi) is a free plug-in that allows you to clone a physical machine to virtual machine - and perform the neccessary "system reconfiguration" required to make it bootable. Without this tool or a commerical P2V tool the virtual machine would just give a "blue screen of death"