I recently moved a Sawtooth G4 to PC ATX (coolermaster) case to cut down the heat and noise of the old case.  This involved replacing the original power supply fan with a quieter fan and installing front and rear 120mm fans.  I have a 1.6ghz G4 from Giga Designs with stock fans on heatsink, those fans combined with the two 120mm fans made this case mod noisy.  So I decided to water cool my system.  While looking I came upon this http://www.xoxide.com/thermaltake-silentwater-lcs.html which is the Thermaltake silent all in one water-cooling system.  The brackets included allowed me to secure to my processor without any modifications and installation was easy.  I took out both 120mm fans, front and rear, with the water-cooling radiator and fan placed in the rear 120mm slot.  It is much quieter now, and super cool!  It took me 20 minutes in all, and it works like a charm.  Cheapest solution for mac water-cooling.  Can't post pics since I donít have digital camera.  Just wanted to let everyone know this is the cheapest and best solution for mac water-cooling if you have a G4 in ATX case.
PowerBook: 1.67Ghz HR Powerbook 2GB RAM 100GB HD 128VRAM
Sawtooth: 1.6Ghz Giga Designs Thermaltake Silent Water Cooled G4 Tower in Cooler Master Case 1GB RAM 300GB HD w/Sonnet ATA PCI Card ATI Radeon 9800 pro 128VRAM