This is for people who have a dual boot installation of Ubuntu and Window (XP or Vista). When booting you will see that Ubuntu has created a boot menu that allows you to select an OS to start.
Get the help here
Start Ubuntu. Open a console (menu Applications > Accessories??? > Terminal ) and type the following:
sudo gedit /boot/grub/menu.lst
You might have to type your password and after that an editor will open with a file. Search for the line that says
## ## End Default Options ##