diskutil list >> find your leopard installation volume # and partition #

example :
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *149.1 Gi   disk0
   1:                        EFI                         200.0 Mi   disk0s1
   2:                  Apple_HFS Leopard                 148.7 Gi   disk0s2
Leopard is Disk0s2

umount -f /Volumes/yourleopardvolumename(Leopard)
cd /usr/standalone/i386
dd if=boot1h of=/dev/rdisk0s2 bs=512 count=1
fdisk -e /dev/rdisk0
fdisk > update
Machine Code update.
fdisk > Flag 2
Set Partition 2 Active.
fdisk > w
Writing MBR Sector 0
fdisk > q
./startupfiletool /dev/rdisk0s2 boot
reboot and install should work