Id goto to Netplus computers in ossie park - much cheaper.

If your doing alot of encoding then the quad core is the way to go... but if u can wait a month - the new quad cores are coming out so id go with them... the Q6600 is nearly a year old now...

Get 2GB x 2 stick of generic ram
Get a decent branded power supply - a Corsair 620 is very good.
If you like to play games aswell... then invest in a new 8800 GTS 512 MB G92 chip. Foxcomp computers sell these online for as little as $400.
Get a Gigabyte X38 chip motherboard.

PLE are prob one of the most expensive shops in perth at this stage