I guess, we all faced this some time or the other. A dailog pops up with the message "Do you want to restart your computer now?". And there are only two options - 'Restart Now' and 'Restart Later'. I am in the middle of my work and click 'Restart Later' button. After sometime, the pop up comes again asking the same thing.. I am tired of clicking 'Restart Later' button. What happens if I ignore the popup? Well, I tried it once, and lost all my work.. the computer restarts without your permission...

Microsoft boasts so much about usability in their products.. but this really, drives people mad. This annoying popup comes again and again until you restart. Even after you restart, you never know when you would get it again. The other day, I was downloading some real big files and doing some background work. I left my computer un attended for some time as those tasks don't need my presence. When I returned, to my shock, I could see the windows getting restarted.. so many hours of work just vanished.. 

I finally decided to fight the annoying dailog box, and successfully got rid of it. You could do change the reminder time interval by doing the following:

Change the Setting to 'Enabled' at Start / Run / gpedit.msc / Local Computer Policy / Computer Configuration / Administrative Templates / Windows Components / Windows Update / Re-prompt for restart with scheduled installations. And give the time interval (minimum 10 minutes and maximum 1440 minutes, i.e., 24 hours).

If you rather want to turn it off completely for that session, you could do so by Start > Run > services.msc > Automatic Updates > Click "Stop".

If you want to do some geeky stuff, try the following:
1.Run regedit
2.In [HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU]
3.Edit > New > DWORD: "RebootRelaunchTimeoutEnabled" with a value of "1"
4. Edit > New > DWORD: "RebootRelaunchTimeout" with a value of the time in minutes until the next prompt. "1440" (24 hours) looks like the max. If you input "0" for this DWORD or the former, it will default to 10.

Well, this was not working on Win XP home edition, check this link if you are running on XP Home.. http://computer-vet.com/weblog/2005/05/20/windows_automatic_reboots.html

Regards,
Surya