In the tiger install disc, if you go to system/library/packages and click osboot.mpkg it starts the installer that you would find if you restarted your computer and booted into the dvd, but i did that with the leopard disc and its not working, i have the 9A499 version of leopard, i can't burn it because i don't have any dvd dl and i don't want to do the way where you copy it to a partition and boot into the partition, has anyone found a way to start the installer from the dmg

you can't if you aren't running leopard already, that package is for leo's installer app

Best way to install is to use Disk Utility to Restore the dmg to a partition and boot from that partition.