Computer help $1000-

Build of course.

If you're playing this to mostly play games at high forget the i7 and get an i5.

HD 7850 is a good mid range card.

I recommend buying your stuff off newegg.

When buying a PSU make sure you get a trusted name brand.

Just some basic tips.

Boy things in Australia are a little expensive  

Anyway here's a build I put together. Keep in mind this does not come with an Operating System, please tell me if you need one.

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-3570K 3.4GHz Quad-Core Processor ($235.00 @ Mwave Australia)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($36.00 @ PCCaseGear)
Motherboard: ASRock Z77 Extreme4 ATX LGA1155 Motherboard ($145.00 @ Mwave Australia)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory ($59.00 @ Scorptec)
Storage: Western Digital Caviar Black 1TB 3.5" 7200RPM Internal Hard Drive ($115.00 @ Scorptec)
Video Card: Gigabyte Radeon HD 7850 2GB Video Card ($255.00 @ Mwave Australia)
Case: Antec Three Hundred Two ATX Mid Tower Case ($77.00 @ Mwave Australia)
Power Supply: Corsair 600W ATX12V Power Supply ($89.00 @ PCCaseGear)
Optical Drive: LG GH24NS90 DVD/CD Writer ($22.00 @ PCCaseGear)
Total: $1033.00
(Prices include shipping and discounts when available.)
(Generated by PCPartPicker 2012-08-27 12:53 EST+1000)

An i7 is NOT worth the money for gaming, you won't benefit from Hyperthreading. It's better to go with an i5 and spend the money you save on a beefier GPU.

Is there any chance I could get someone to build it for me? I don't wanna stuff it up?  

You could probably take the parts to a local computer shop and get them to assemble it for you.

However, you're missing out on half the fun!   There's so many tutorials online now that you can't mess it up!

thanks, I'll look into it