A simple problem with a simple answer, I wanted to be able to reboot my Linux desktop PC and reboot into another OS from within the already booted OS
In Debian there is a little application called grub-reboot, this will allow the root user to select what menu item grub defaults to on the next boot. edit the following file to look something like this, replacing dthomas with your username.
sudo nano /etc/sudoers
dthomas ALL=(ALL) NOPASSWD: /usr/sbin/grub-reboot
now create a menu item on KDE this is achieved by right clicking on the "K" menu button and choosing the "edit applications" and just adding an entry with the command
sudo grub-reboot 2
to reboot to the 2nd entry in the grub menu and grub-reboot 3 for the third and so on.