Boot into Ubuntu, open a CLI (Command Line Interface) and type
sudo update-grub <Enter>

This should update your Grub2 configuration file. I noticed that when I first
installed to 10.04 the install process failed to properly configure Grub.

BTW, I'm still running the last version of 10.04 Beta. I get regular updates and
when I tried upgrading to the final version, I got a message saying I am already
running the latest version. I'm not really keen on the idea of doing a clean
install, considering all the apps and extras I have installed. Can anyone give
me a good reason why I should not keep on truckin'?