After performing a physical to virtual conversion one of the tasks you have to do is to set the IP address of the new virtual NIC. When you do this you then get a warning message saying the IP is already assigned to the physical NIC, Windows 2008 is better than 2003 as it at leasts removes it from the old NIC for you.

All the same this seems a bit illogical, that physical NIC is no longer connected to the server so why should it keep the details? Also it can cause confusion for some services as the details are still stored in the registry even though the NIC isn't active. Should you have a dig around there's no trace of it in the Device Manager though, and hacking bits out of the registry isn't a great idea.

The process for removing the old NICs is actually quite simple and I found a good explanation of how to do it here:

http://www.tacktech.com/display.cfm?ttid=419