the best method to update a
working Intel system like yours is
>>manually <<. it takes about 10 minutes, and you should have no problems whatsoever.
if you are using gma900/950 kexts, or Callisto and Kovergs,
everything that you have working, will remain working. the new (and mainly useless) 4.6 kexts do not replace your working drivers. if you upgrade to the x1600 the 4.6 ATI kexts and Extensions are backed up for later possible use.
"why?" you've given the best reasons why yourself.

good luck.
p.s. don't you just need the 10.4.3 AC97 and NetworkingFamily kexts to get sound and ethernet working with that board? they might not be the ones, but i'm pretty sure that board is the one
>> bofors << used in his computer. i can't see him buying something without a guaranteed solution available.
Thanks but my board is actually the media edition, very close, slower LAN 100 vs 1000 but better audio, although I will never use it as I use FW Audio.
Have some quirks though that I am trying to sort out within the next 10 days or so as you can see here: