ok, you have your XP on c: (hda).
After that you installed linux and used Linux_Bootloader
to manage your OS:es.And now you want to delete your windows-partitions, but feel that you gonna lose your linux to because your mbr will dissapear ?
I would use my slackwareOS, via 'fdisk' to delete XP_partitions.
Then i would do/run a new 'liloconfig' (if that boot loader is to your liking) to reinstall the correct MBR (kind of
).
I haven't feelt the need, yet, to try this,
but i believe that it should work