Eugene's observations

Windows Update normally (should) run automatically and sometimes will require a reboot after installing patches. At such times a nag message will popup every 10 minutes asking you to either 'reboot now' or wait another 10 minutes, at which time you will be interrupted again. What if you are watching a film or have other reasons for not wanting to reboot immediately ?

If you click Start, Run and enter
sc stop wuauserv
The service that causes the prompt will be gone until after your next reboot - which you can do at a time of your choosing.

If you are running XP Pro you can increase the delay between nags permanently by changing the Group Policy:
* Click Start, Run and enter the command gpedit.msc
* Select Local Computer Policy, Computer Configuration, Administrative Templates, Windows Components, Windows Update
* Double-click Re-prompt for restart with scheduled installations
* Change the value to the preferred number of minutes between nags (max 1440)
* Close the Group Policy Editor
* Click Start, Run and enter the command gpupdate /force