getting sound working in yellowdog 4.0 is actually fairly trivial.
it requires running yum update, updating your yaboot.conf to reflect the newly built kernel (to check version just cd /usr/src && ls -lrtd, run mkofboot.
finally open your /etc/modprobe.conf and everytime you see the string "dmasound_pmac" replace it with "snd_powermac" <--- this takes 2 seconds
My sound is working fine now. I disable artsd out of habit because it is a resource hog. ( i am running gentoo on an athlon xp notebook as well, so sound being this easy to enable is nothing. On my athlon notebook i have to use a wrapper to even get my wireless card to work which utilizes a microsoft windows driver, and i have no direct rendering support.. My iBook runs flawlessly and only took 45 minutes to do so including getting xmms, sound, firefox, BitchX, etc working properly.
Overall my first impression with Yellowdog is quite positive. I will be checking out these forums more often and hope to learn and help out alike.
to summarize, my setup:
sound tested and working
500mhz g3 iBook Dual USB 12"
512MB PC133 40GB HDD
Yellowdog 4.0
missing:
arts (kde sound server.. you do not need this 99% of the time)