The screen that you see will be it booting from the OS X CD in Verbose mode - when the text stops scrolling, does it say "panic - we are hanging here" at the end? If not, then you just need to give it time to boot into the OS X installer. The modern hard drive will work in the Beige G3 - you should try installing X with the drive connected to the internal bus and the first 8 GB of the drive as the target for OS X installation. XPostFacto often doesn't work when you have PCI cards like that installed, you should try removing everything except your video card (you need a separate video card for it to work with 10.3 or 10.4).