Updates are best done one at a time, in my opinion.
Reinstall with the 10.6 DVD again, and once installed ignore all the other offered updates (deselect them) and only update to 10.6.8. If that sucessfully restarts, then choose the other software updates one by one. That's my update voodoo rule No 1.
Don't use you computer while updates are being done. Just wait. That's my voodoo rule No 2.