This update in the end worked fine. But had me worried for awhile when updating.

I did the usual:
1. Booted in "Safe Boot Mode" ( Hold Shift key down when booting)
2. ran OS 10.5.7 install. Took 10 to 15 minutes to complete , a bit longer then most for me. Then clicked restart button when prompted , as usual.

This is where I began to wonder. Upon click restart all the icon disappeared like they should but hung at the desktop backround to 15 to 20 minutes. I almost turned it off when the screen finally went black and began to boot. Did the usual double boot then another 5 minutes and it was up and running. I immediately ran "Repair Permissions" with Disk Utility and ll seems fine. I is , in fact, faster on the internet although in Safari it won' let me add feedback on Versiontracker but worked in Forefox okay.
Anyway this method has worked for me for every update since the beginning of time. Well Mac time anyway. This update just took way longer then most, so BE PATIENT!!! Big time PATIENT.
I installed on a iMac 2.0 PPC ALS enternal HD where I test everything before putting on my internal HD.
Good Luck