This machine's been quietly running DNS and outbound SMTP for the local LAN, together with a few other bits and pieces (webserver, netatalk appleshares etc) for almost a decade now, on RedHat 7.1 (I think it started life on RH6.2, or possibly 5.x)
It has never, in all that time, crashed/hung or given any murmur of trouble.
So here were the steps:
1) Create a new VMWare Player virtual machine (I had a suitable template handy specifying one 60GB IDE disk and one NIC)
2) Boot the VM using the Fedora Core 2 Rescue Disk .iso, starting networking (static ip 10.0.1.101 on same subnet as physical box) but skipping trying to find a Linux installation to recover (because it's blank).
3) Start netcat listening for inbound data from the physical box elsewhere on the network:
nc -l -p 9000 | dd of=/dev/hda bs=128k
4) Boot the physical box using the actual FC2 rescue disk and duplicate the disk across the LAN to the VM:
dd if=/dev/hda bs=128k | nc 10.0.1.101 9000
5) Wait (well, go to the local car boot sale actually - got some very nice 1958-vintage OS map sheets of the local area for a couple of quid each)
6) When completed, shutdown the physical box (otherwise on booting the VM I'll get an IP clash)
7) Reboot the VM, let kudzu do its magic with spotting a different type of NIC than the physical box had, and bingo - a virtualised clone of the physical box.
Incidentally, I had configured the VM to use the 'vlance' virtual NIC rather than the e1000.
This has saved me the grand total of 76W, or 1.8 KWh/day - about £100 per year.