Start > Control Panel > System and Maintained > Administrative Tools > System Configuration

This area lets you control Windows behavior on startup. The options presented are as follows:

Normal Startup – Load all device drivers and services (normal behavior)
Diagnostic startup – Load basic devices and services only
Selective startup – Load any specified group of items: system services, startup items as well as an option to use original boot configuration

The Normal Startup option exists for you to set things back to normal again after choosing either diagnostic or selective startup options. The diagnostic startup option starts only basic services and drivers and is intended to help rule out basic Windows files as the source of a problem you may be investigating. Naturally, selective startup lets you be a bit more granular in your decision to disable how Vista starts up.