Budget gamer pc

^ I would suggest these changes...
1. RAM - Don't use 3 RAM sticks on the boards which have 4 slots...use either 2/ 4 sticks to get Dual-Channel config...if you fill up 3 slots with those sticks, then you will loose Dual-Channel config...those RAM sets are specially made for i7 9xx(X58 mobos)...And also for gaming 4GB would suffice...

2. HDD - You can check out even the Samsung F3 500GB HDD...they are faster and you would save some money there...

3. Graphics card - Now that you have saved some money with the RAM and HDD(500GB is still lot of space and also later on you can add another if you want )
why not get the HD 5850 ? If you game at high resolution, then it would be a better option than the HD 5770...

And what PSU have you selected ?

Whats the difference between the HD5850 and 5770? is there much
because theres a $200 price difference

will the 4gig perform better than the 6gig?

case is just a generic case with a 650wat psu

altogether its cost me just under $1000 aus

^ Yes...there is a significant performance difference between the 5850 and 5770...
For resolution say 1080p, the 5850 is better suited...
But if you dont game frequently and play at lower resolutions - less than 1080p, then you can stick wiht 5770...

And Yes when you populate 4GB - 2 sticks on that mobo, it will run in dual-channel so it will be faster...but when you populate 3 slots, then you will loose dual-channel hence it will run slower...

you have to be careful when choosing the PSU because that is one of the main component of the PC that you shouldnt skimp on - in terms of quality...

I agree with Gkay09 so far...
which PSU?

Good call with the 5850.

Quickly, go to:

http://www.techbargains.com/product/5850

5850 is $251.99 w/ free shipping.

Assuming it is not a 650 Antec Earthwatts, which has been included in some cases, a generic "650W" PSU that is included in a cheap case will likely be a Chokemax, perhaps capable of 400W-450W, and perhaps with poor ripple and noise; in short, a unit not fit to power a computer. Choose a PSU with full range active PFC (no little voltage switch) and 80+ certification. For a single HD5850, you only need 450W.

my old comp was

AMD Athlon X2 5600 2.9ghz

CORSAIR TwinX 1gig x 2 (2 Gig) DDR2 XMS2-6400C4 800mhz

GIGABYTE GA-M51GM-S26

ATI HD3870 PCI-E 2.0 512MB 256-bit GDDR3 775 MHz

case is. x-sonic atx-p4 600WD

is there much there in performance difference..
or should i just wait and save...

For modern games (i.e. not something old like Diablo II) there's a huge difference between a 955BE and an Athlon X2 5600+, or a HD5770 and HD3870. Only you can decide if it matters.
...but please note the various suggestions, e.g. getting 2x2GB RAM sticks, since the 3x2GB you listed are for Intel triple-channel CPUs and mobos.