Mac os 10.5.8, Leopard, is the maximum os for the machine.
1) Use TenFourFox for surfing the internet.
TenFourFox -- It's a port of the latest FireFox to run on older hardware and software.
"World's most advanced web browser. Finely tuned for the Power PC."
-- works for me on 10.4. Supports 10.5
http://www.floodgap.com/software/tenfourfox/
alternative download site:
http://www.macupdate.com/app/mac/37761/tenfourfox
Turn on pipelining. This will allow Firefox to make simaltaneous requests to the server. Chrome has pipeling turned on. Some sites could fail to load with pipeling set on. The site will be old. See "Increase pipelining" in:
http://www.hongkiat.com/blog/firefox-optimization-tips/
2) Max out the memory.
give these folks a call
http://eshop.macsales.com/shop/memory/PowerMac-G5-Memory
3)
I tend to think dashboard is neat, but not neccesary for my everyday workflow.
it is possible to enable and disable it as needed,
by entering the following commands into the terminal:
-- To turn Dashboard off:
defaults write com.apple.dashboard mcx-disabled -boolean YES
-- To turn Dashboard on:
defaults write com.apple.dashboard mcx-disabled -boolean NO
-- You have to restart the Dock after making either change for it to take effect:
killall Dock
Bye Bye Dashboard
http://www.kainjow.com/kermitsoft/downloads.html
Disable Spotlight, Bonjour and Dashboard:
http://discussions.apple.com/message.jspa?messageID=8749558#8749558