It has been a while since I needed to convert a Centos 4 machine. I do remember (very fuzzy) needing to modify fstab or grub.conf to get them to boot. I would try one. Even using workstation as the target you will get a reasonable idea of how successful it might be. You may run into some that don't. LVM will convert to standard disk devices. I would give a try to the Beta Converter 5 as well as the older 3.03
I do remember that I used netcat or nc quite successfully. Use a rescue disk with netcat on both the physical and the virtual machine. netcat basically reads the disk and streams it bit for bit to another network location. At the receiving end netcat writes the stream to disk.