You could use the rescue option of the first boot disk, or the live disk you mentioned.
With the install disk rescue option there is a menu option to mount your system under boot. Select this option.
Next cd to the /mnt directory and make it your new root.
Be sure to to watch the output of the lilo command. Each section (stanza) is printed out. If there is an error, the MBR will not be updated.
If there is a problem, you can create a lilo boot floppy which will allow you to boot up to linux from a floppy disk.
Edit the boot= line of /etc/lilo.conf so that it contains 'boot=/dev/fd0'.
mount a floppy in the drive and execute '/sbin/lilo' again.
Sometimes there will be a problem with trying to get the MBR updated with XP and the NTFS drive. If so, you can google for 'Lilo NTLDR boot howto' for a number of HowTo's on how to setup the XP's NTLDR.exe program to boot linux.