Question : Problem: Best gaming pc for AUD $2500 (USD $2027)

Best gaming pc for AUD $2500 (usd $2077)
Something along the lines of

(prices in AUD)
Gigabyte DQ6 $280
A-Data 2GB DDr2 800mhz $189
E6600 $305
Samsung SATA 16mb 500GB $162
WD Raptor 150gb $300
Pioneer SATA 18x 212D $50.00
Gigabyte 8800GTX 768MB $863
Gigabyte Aurora 570 - $220
Coolermaster I-green 500 $121
Viewsonic 22" LCD $399
Logitech MX 3200 $140
Logitech X530 5.1 $85

What things that are not nessesary?

Answer : Problem: Best gaming pc for AUD $2500 (USD $2027)

Most of your components are good.  If you intend to overclock (the E6600 is exceptional in this department, with 50% being a reasonable expectation), you have a good motherboard, but I would suggest known quality RAM, such as OCZ, Patriot, Kingston Hyper-X, Crucial, Corsair, or Mushkin premium models in dual channel modules.  2GB is more than enough for gaming, and WinXP can't use more even if you have more.  A good cpu cooler would also be recommended if you overclock, and the Zalman 9700 is considered one of the most efficient, though there are others that are good also: http://www.xbitlabs.com/articles/coolers/display/zalman-scythe.html

I would go for a more powerful power supply, since the 8800 is very demanding and 600 or more watts with high current is more reasonable to plan for future expansion.  Seasonic makes a very good model http://www.newegg.com/Product/Product.aspx?Item=N82E16817151030

I would also split up the hard drive into two - a smaller, faster, 74GB Raptor for the OS and games you commonly play and a Seagate 500GB 7200rpm SATA2 drive for storage and backups.  If you tweak or try out new drivers, you may find yourself with an OS that is hosed.  Making periodic snapshots of the boot drive enables restoring to a working state very easy.

If you don't intend to overclock, a cheaper MSI P965 motherboard would work, but it would be a shame to hold back the E6600 when you pulled out all the other stops.