Do you mean you are stuck in the dreaded loop? Microsoft have this to offer:
The update is not installed successfully, you receive a message, and the computer restarts when you try to install an update in Windows Vista and Windows 7 If you only mean, on the subsequent reboot or start, Windows 7 does the same thing, depending on the update. With certain updates, it is neccessary for the OS to close the particular service or running program, before it can update. The method used is on a reboot or restart.
The only way to stop it would be not to allow the computer to install updates until you are ready for them.
In the Windows update feature, you have two features which could accomplish that.
Check for updates but let me choose whether to download and install them or
Download updates but let me choose whether to install them.
The second option can be a bit of a nuisance on a low performance machine, if you are in the middle of intensive internet work and the extra load is imposed on the system.
After you have accepted the installation of updates, the window will, in the appliceable circumstances, request a reboot. ( and the subsequent message) You can, of course, reject this request until it is more convenient for you.
A final way would be to switch of updates entirely and download them manully at times when it also suits you.