From our Microsoft TAM:
Have you ever wanted to be able to install Microsoft security updates without having to reboot your servers? With Hotpatching, you can do just that for selected updates. Please read on for details.
Using Hotpatching Technology to Reduce Servicing Reboots
http://technet2.microsoft.com/windowsserver/en/library/8bf7c6e4-3175-43bd-a67a-827ff3a586011033.mspx?mfr=true
How to use HotPatching to install security updates for Windows Server 2003 Service Pack 1
http://support.microsoft.com/kb/897341