I have a lovely HP G6 Nehalem server which I want to get up and running asap... but the second CPU hasn't turned up yet. Does anyone know if it is safe to build the O/S and stuff before that arrives, and the plug the new CPU in then, or will I cheese my server and have to rebuild?

I found this link for Server 2003 which implies that it is ok
http://support.microsoft.com/?kbid=309283
But if anyone has actually done this IRL (even if it's on Vista or something) then that would make me feel much better about it!

As long as you install on a multicore cpu you'll be fine. I've done it loads of times.
It's only if you installed on a single core single CPU you'd have issues.

Woot! you are the man.

Just make sure the 2nd CPU is the same stepping (if not it works but you get loads of error messages in the logs)

Thanks for putting the nightmarish memories of my first dual CPU system, (Pentium 3's) back into my head