recover the Windows XP in bootcamp

Yesterday, I tried to install Ubuntu on an external usb disk for my new macbook (already dual boot with Windows XP and OS X), but I forgot to check how Ubuntu installer would install the Grub, which turns out to make my Windows XP on the internal disk unbootable with a message like this: " GRUB hard disk error".
After some trial and correction, I recovered the XP with following steps:
1. Boot the laptop from XP installation CD
2. When prompted, press R to enter the recovery console
3. fixmbr
4. fixboot