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