First off you need a motherboard, which is the big thing you stick everything on. Then you need a CPU that fits the motherboard, some ram and most likely a gfx card. As far as storage goes you get to choose between HDDs (standard, slower and larger) or SSDs (high-end, faster and smaller, hella costlier too). You'll need a PSU to power everything and a case to house everything. /easy
Mobo: look for a P67 board, that's the chipset Intel uses for most of it's consumer CPUs now. Gigabyte's GA-P67A-UD4 is an awesome board and it supports SLI or crossfire, if you will ever want to run multiple gfx cards in the future. (costs ~170 bucks)
CPU: if you want something awesome the i5 2500k is unlocked for all your OCing needs, so that if you ever feel the need to juice more power out of your PC, well, you will be able to (costs ~220 bucks)
RAM: any 1600MHz CL8 or even CL9 ram should suffice. Although CL8 (or lower) is better than CL9, I guess you could save heaps (2*4GB 1600MHz CL8 costs ~70 bucks)
GFX: Nvidia 560Ti, because I can't be arsed to support AMD's shitty software and lack of innovation any more (costs ~210 bucks)
HDD: Spinpoint F3 1TB, because SSDs aren't worth it and it's awesome (costs ~150 bucks)
SSD: alternatively, if you want something faster, you can get a 64GB Crucial m4 (costs ~120 bucks)
PSU: anything that can handle 700W and looks decent, e.g. something from Cooler Master would come about 80 bucks
Case: Fractal Design Core 3000, because it's epic even though it looks plain. (costs ~70 bucks)
About 900 bucks if you buy it in the US, dunno about Aussie prices. You could always lose the Spinpoint F3 HDD in favour of a Hitachi 500GB and practically shave off 70 bucks but lose some performance, similarly you could opt for a weaker cpu or gpu. Talk to @
Doc or @
Sir Ragealot about finding a decent store, I dunno anything about your options in Kangarooland.
Edit: I didn't add a DVD drive, because you simply don't need it, at least I don't. You can install Windows from a USB key easily and pretty much nobody watches movies from DVDs nowadays. So yeah, 20 bucks saved.