Boot the CD

Mount the XP partition (probably /dev/hda1)
Change the read-write mode

^ Both of those can be done in KDE by right-clicking the drive icon and choosing those options. If the drive is NTFS, it will complain when you try to enable write mode.


Assuming it is FAT32, you would then run these commands from a terminal

su
cd /mnt/hda1
kedit boot.ini

The default boot.ini file would look like this:

[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINNT
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINNT="Windows XP" /fastdetect