I went down to my local computer store today – Zip Computers and bought another stick of RAM (Kingston 512MB, PC3200, 400MHz, AU$109). Same type that I bought in Sydney, but a different brand.
Opened up the Mac, popped it in and heard the wonderful Mac bootup sound.
It works perfectly.
I haven’t had a chance to go back into that other computer store and return the obviously faulty RAM that I bought from them yet, but I will soon.