Most of the times any Windows update you apply to your computer requires you to restart your PC. I definitely get quite fed up with the frequent nags to restart the PC. Previously I had written a tip on how to disable restarts after Windows update.
However, if you want to do it the easy way, Postpone Restart is a handy utility, which can postpone restarts after a Windows update has finished. Postpone restart is a small tool but can be useful for those nagging times.
Postpone restarts works with Windows Vista and Windows 7, there is no support for Windows XP yet.