Repair Windows 7 mbr

I have a laptop, my hard drive into two partitions, one with Windows 7, the other with Ubuntu.
Yesterday I formatted my Ubuntu partition (which really helped me more) to save XP Instead compatibility issue. Except that my XP cd is too scratched, he has planted the setup, but the rub is that he has screwed up my Mbr ...
So I boot the liveCD ubuntu, have re-installed, history of having an OS and a mbr, except that in grub when I chose Windows Longhorn j'atteri to a black screen, and I must reboot ( I think the mbr reminds himself that there had XP, but not booted because it no longer exists.) and nothing allows me to access my Windows 7.

Does anyone have a solution. So that I can deleted my XP MBR, and can choose between Seven and Ubuntu from Grub?

How to repair Windows 7 MBR?

1. Boot from Windows 7 installation DVD in the drive.
2. Then Choose your default "Language", "Time", and "keyboard Input" on the first window screen. Then click next.
3. Click on "Repair Your Computer" to gain access to the System Recovery window. Then select "Command Prompt".
If you had Win 7 initially installed in the C partition, typing

"bootsect /nt60 C:\"

in Command Prompt to run.

Or you can type "bootsect /nt60 SYS" or "bootsect /nt60 ALL" in the Command Prompt to repair your system partition or all partitions.
4. Restart your computer and your windwos 7 can appear again.