It becomes a bit tricky in Ubuntu 9.10 to rewrite MBR because of the newer version of GRUB: GRUB 2. You can follow the steps here, its pretty straight forward.:\
https://help.ubuntu.com/community/RecoveringUbuntuAfterInstallingWindows\ \ Following this procedure, you’ll recover your Ubuntu system. Incase there are any discrepancies in your Windows system, updating grub from your native ubuntu (the one on your hard disk) might help\ \ sudo update-grub