I was trying to install 10.2 on a B&W G3 400 at work. Everytime that I tried to install, the install would hang at the end, just as the text would say "under one minute". Really annoying. I tried installing about 8 times and it would hang every time.
At first, I thought it was because the HD was SCSI and that the Adaptec card was giving issues, so I removed it and replaced with with a new IDE drive. No joy.
I decided to replace the graphics card (this seemed to work on one computer in the past with 10.1). No joy.
I then checked out the RAM. It was Samsung. I promptly ordered new RAM from crucial. This fixed the problem. 10.2 seems very (maybe overly) picky about the RAM it will use.
Now, the first thing I do with any Mac I need to work on, is check the RAM.