I recently put a fresh install of Tiger on my Power Mac G3 (Blue & White). It has 512MB of ram and a 20.GB Maxtor HD that I took out of an old 500MHz G3 iMac. The screen that it freezes up on is when it shows the grey apple logo and the little turning graphic below it. It will load for a few seconds, and then a black box will replace the apple logo and the turning graphic will stop. I have left it on for about 20 minutes after that to be sure that it's not just taking it's time or anything. Any thoughts?
Hold the shift key down at startup in order to enter safe mode. It might boot up that way, and then see if it will restart ok. I don't remember if you can repair permissions or not in safe mode, but if you can, do that before restarting. You repair permissions by clicking on your system volume while in Disk Utility--which is in the Utilities folder in the Applications.