Subtitle: Really, I mean it, backup your stuff.
Having installed the new disk, my task this morning was to make recovery disks and image the main disc on the server. Sadly I was a day too late, as the other disc has failed. The one with the OS on it; my domain controller and mail server. Bugger.
Currently I'm rebuilding a spare with Exchange, just so I can get email going again. I've also just ordered a RAID controller and 4 discs, so when they arrive I'll install the OS onto a RAID 5 array (or possibly 0+1 - I haven't decided yet).
On the plus side, the .NET 2.0 framework has shipped, so I plan to upgrade the web server this weekend. That means the site for the Wrox Press Beginning ASP.NET 2.0 site will be publically available.