i have the same problem , leopard installs to the 3rd partition on hard disk (1st is winxp ,2nd vista both ntfs) after install reaches 100% ,reboot (remove dvd from tray during boot loader) leopard starts loading and reaches a point where it is loading the xp and vista partition (i guess by what it says) and it stalls just after ,waited 2min a little hd activity and then nothing forthe next 30min.
i tried changing kext's deleting kext replacing ,onboard lan on/off ,sound on/off ,tiger is installed on a seperate hard drive it runs fine. i am gonna try switching leopard to the single disk and tiger on the partition ,as i have tried everything else in many forums.

amd sempron 3200
ide maxtor hd
ide west dig hd
asus m2v-mx<green>
ati hd2400 video card