Having actually run the MINT installer now, I realise that I *did* malign it. If you choose the 'manual' option on the partition page, then later on you get an almost hidden 'advanced' button. This allows you to choose where to put the bootloader and also gives an option not to install one at all
So thats what I did - no bootloader, and I reused my existing VL5.9 partition for the MINT root partition. I unchecked the 'format' box (since it was already EXT3, I thought this might be ok). The install finished and I rebooted into VL6 and ran VASM to rewrite LILO to the MBR. Rebooted, and the LILO menu now showed XP, VL6 and an extra entry called 'Debian...'. So VASM had detected the MINT O/S and created an entry for it.
Did it work ? Of course not
but at least that was a good start (selecting the Debian entry gave me a few screenfulls of text followed by an obscure error message - somethign about xfce4 not seeing an exec line).
So, I reasoned that maybe I should have formatted the partition after all. SO I went back and redid it and everything seemed to go ok. But, when I reran VASM it no longer saw the Debian partition
(fdisk -l still showed it - or showed that there was such a partition).
Is this something to do with me losing the partition boot flag (there from VL5.9) when I formatted it ?
I tried VASM from text-mode, but same result.