I am new to this forum, but have been wanting to mod a powermac into a silent "cube-like" music server/digital photo frame in my living room. I just picked up a g4 AGP 350/576/10/dvd used for $165. It is so noisy--particularly the PSU hum (not the fan)and the little fan on the ati rage pro!!! I am used to an imac (flat panel 15") and an ibook g4.
the way i see it the secret of the cube is that it has an external, quiet PSU. if you dont put all that heat in the same box as the cpu and other electronics, the cooling problems are much simpler. here's the plan
Step 1 replace ati card with radeon 7000 with heatsink only. replace cpu with powerlogix g4 800 with heatsink only (fastest without fan that i could find)
step 2 separate cpu from PSU by removing all parts from case
step 3 create separate enclosures for cpu,psu,drives
step 4 eliminate fans completely (except for possibly just slowing down psu fan)...add heat sinks with major ventilation to all 3 enclosures.
step 5 splice in longer connections to allow PSU to be out of sight and away from workspace (12"-24")

step 6 possibly ....
replace psu with aftermarket quieter one....????is this possible???
any of you experienced guys have any suggestions i would appreciate them