Hi Henryutd, building your own pc is definatly beneficial. I've built every computer I've ever owned, and about 2000 others as well.
If you buy one of those dell / hp / ibm packages you see at harvery norman around they may appear cheaper - but you can't upgrade the pc easily. (i've built many of these as well).
As you're in australia, I can point you in direction of many a good website. The best of which is
www.auspcmarket.com.au - next day delivery anywhere in australia - awesome servers and huge range. prices include delivery.
www.staticice.com.au is a good way to find the cheapest prices
what you need to build your own computer is simple.
Motherboard (aka Mainboard)
CPU - make sure the socket is the same as the Motherboard
RAM (aka Memory) - again, make sure you are getting the right one for the motherboard
Video Card
Case
Powersupply - this is a big one, you need to make sure you are getting enough power.
Hard drive - most websites in australia refer to this as "Storage"
Floppy drive
CD/DVD drive - get a dvd burner - they're just as cheap
Most motherboards come with onboard sound, but I would recommend you get a sound card as well - better quality, and better for games.