BootNow is a separate free product (available on the BootIt NG download page) which allows you to select the boot item from within Windows 9x/ME/NT/2000/XP/Vista/Windows 7. By double-clicking a BootNow item, the system will shutdown and restart with the selection you chose.
BootNow also has an option to run idle in the system tray waiting for the system to hibernate. When the system hibernates, it will automatically set up BootIt to boot the prior booted boot item so that any hibernated OS is resumed without the option of booting a different OS. This is desirable when partitions are visible across different OSes and you use hibernation. It prevents changes to the partitions the hibernated OS has access to as recommended by Microsoft.