There is no need for such a drivers download. All the drivers and softwares you need are built into the operating system either OS9 or OSX. Get yourself and OS installation disc and you will be up and running.

Exactly.. As simple as that.. So just get the installation disc.. --end of story--

PS: excluded some of 3rd party hardwares, like probably your scanner, printer and etc. Those need install the driver, if you don't have the disc, just get it online. Google is your God. 

Shouldn't be a problem.   However, the farthest I went was popping in the installation DVD and my iBook G3 is able to boot up with 10.4 installer.   Never went beyond that I am happy with MacOS X 10.3.   Also, is your iBook able to handle MacOS X 10.4?   This is my concern too that stopped me for going further.

I suppose it depends on which revision G3 ibook you have as well. For instance, I wouldn't even wanna run OS X 10.4 on my iBook G3 300Mhz... so those are the things you might want to consider. An earlier version of OS X would be more prudent for performance reasons.