hi - a few things for G5 and ProTools:
ideally, make sure ProTools is the only application running. Safari will slow things down, especially if Flash isn't disabled..
main thing to remember is to disable hard drive spindown and sleep mode in the Energy Saver Control Panel.
I'd recommend using a free app called Caffeine for Mac that will let you choose when to delay sleep, screensaver etc.
Digidesign say to do the following:
Configure System Preferences
Optimize Energy Saver
Turn off Airport and Bluetooth
Disable Time Machine
Disable FireWire Networking
Disable FileVault protection
Update iLok Drivers
dsable Software Update
more from them on this at:
http://avid.custkb.com/avid/app/selfservice/search.jsp?DocId=349731&ssdFilterCom munity15=1409&ssdFilterCommunity13=0&ssdFilterCommunity11=0&ssdFilterCommunity10 =368&ssdFilter_SearchKeyWord=OSX+optimization&page=1&ssdSearchOperator=0&ssdFilt erCommunity3=1078&Hilite=OSX+optimization