Repair XP Boot Loader

http://www.techsupersite.com/repair_xp_boot_loader.html

First you must reboot the system from your xp cdrom.
Then when prompted select the option to enter the recovery console. Select the installation to be repaired followed by the administrator password.
Type Fixboot and answer yes to the prompt.
Then type in the following commands and leave all spaces eactly as they appear here.
CD \
ATTRIB -H NTLDR
ATTRIB -S NTLDR
ATTRIB -R NTLDR
ATTRIB -H NTDETECT.COM
ATTRIB -S NTDETECT.COM
ATTRIB -R NTDETECT.COM
COPY X:\I386\NTLDR C:\ ( X IS THE LETTER OF YOUR CDROM )
COPY X:\I386\NTDETECT.COM C:\ ( X IS THE LETTER OF YOUR CDROM )
Afterwards reboot

Reference:

1. Boot INI Options Reference
2. How to Perform a Windows XP Repair Install
3. Repair XP
4. Repairing Windows XP in Eight Commands
5. How to dual boot Vista and XP (with Vista installed first) -- the step-by-step guide