The description which appears in the boot loader is a simple text string that can be edited. You will need to load Ubuntu and edit /boot/grub/menu.lst
Google edit + grub if you want more details such as how to change default start option but for your problem it should just be a simple edit of the description string.
To edit menu.lst, start a terminal session.
Before you change anything, make a copy of the GRUB menu file as a backup by entering
cp /boot/grub/menu.lst /boot/grub/menu.lst_BU
Use this file to restore menu.lst if the changes fail.
Edit the menu using the command
sudo gedit /boot/grub/menu.lst
sudo gives you admin rights to edit the file, gedit starts the Gnome text editor called gedit.
When you have changed menu.lst, save the file and exit gedit.