I have the same problem so I used the link on the Macrumors article for the 10.5.7 update. When it was time to restart however, I clicked the Restart button on the installer and it just greyed out but didn't actually restart the computer. I had to hold the power button on my Early Macbook Pro, my computer restarted twice and went smooth from there.
Also, Safari 4 is finally compatible with Hotmail! No more switching to Firefox.
Yeah, my MacPro 2.66 wouldn't restart on its own either. I had to force a shut-down. That made me nervous. But it worked.