I have a very large FOG setup. I run one Master FOG server, then over 500 Node servers positioned throughout the world. All the PC's PXE boot from the local node server and then pull the live IPs from the local satellite modem DHCP server. I didn't build the system, I just fell into it and have been maintaining it. We are using FOG version .28 on all the servers and each one runs on VMware ESXi 4.1. Currently all 6000 plus PC's are Windows XP and in a workgroup. I need to upgrade the PC's to Windows 7 (still no domain) and possibly upgrade the FOG system to a newer version. My initial question is do I have to upgrade all the servers at once or will the .28 version node server work with a new verison on the master FOG server? And will I have to upgrade the node servers at all?