The version of fdisk that comes with Windows
cannot delete or modify the linux partition.

You have to boot into linux, and use fdisk
from there. You can change the partition ID
number to a type that minix can use.

Once you do that, though, LILO may give you
some trouble, because it would still
be there, trying to boot linux from that partition

The usual way to uninstall LILO is to boot windows (or dos)
and type the command FDISK/MBR <enter>
This restores the windows bootloader.

Your minix installer may or may not be able to take it from there.