Ok,
So I ran the script that tells you if your current ESX 2.5.x install will upgrade nicely (meets the requirements), and it reported that things were find to proceed with an upgrade.
I put the ESX 3.0 server CD into my Dell 1850 ESX server, and booted...
...and then followed the GUI install of ESX.
Suddenly, it drops from X-Windows and reports "Install exited abnormally" during the upgrade.
What do I now? It appears that ESX 2.5.x is still fine, but I want to get the upgrade working.
Gerhard