Rescue my Windows XP on Macbook

After install Ubuntu on my Macbook with USB HDD.
Grub installed on disk0, while Ubuntu install process.

Mac OS boot loader seems can not found Mac OS X & Ubuntu as the same USB HDD. It always found the Mac OS X partition.
After Ubuntu boot failed, I boot up my Windows XP by Bootcamp.
System always shows "Grub HDD error".

I found one document in Internet.
http://cha.homeip.net/blog/archives/2005/05/_windows_mbr.html

I know I need MBR recovery to rescue my Macbook.
In my Winclone image about six months ago, I found one file, boot.mbr.

I use dd if=boot.mbr of=/dev/disk0 bs=446 count=1 for a try, but failed.
The Mac OS X partition on disk0 seems locked by OS.
I use "sudo umount -f /dev/disk0s2" to umount the Mac OS X partition, then dd again.

Finally, my Windows XP boot-up screen show up.