Computer Hardware Stores Melbourne

REALLY NEED HELP WITH COMPUTER HARDWARE PROBLEMS!?
I need to buy a 2.4 GHz Processor, 1.5GB RAM and a NVIDIA GeForce GTX 280 or 9 series. Could you tell me what is the best store to buy them from in Melbourne, Australia?
And is it actually possible to upgrade a Processor?
These are my computer details:
I have a Compaq-Presario, SR5140AN
Processor: AMD Athlon 64×2 Dual Core Processor 3600+ (2 CPUs)~1.9GHz
Memory: 894MB RAM
NVIDIA GeForce 6150 SE nForce 430, total memory 313 MB
Integrated RAMDAC
PLEASE HELP, MUCH APPRECIATED!
HP.com/Support and the page for the Compaq Presario SR5140AN,
1.http://h10025.www1.hp.com/ewfrf/wc/product?product=3453790&lc=en&cc=us&dlc=en&submit.y=4&submit.x=9&lang=en&cc=us
Product Information,
2.http://h10025.www1.hp.com/ewfrf/wc/prodinfoCategory?lc=en&dlc=en&cc=us&lang=en&product=3453790
Motherboard Specifications,
3.http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01077676&lc=en&dlc=en&cc=us&product=3453790&lang=en
Motherboard is made by ECS for HP/Compaq
ECS model name for motherboard is MCP61PM-HM
HP/Compaq model name is Nettle2.
Looking under the Part/Feature column heading, and scrolling down to CPU/Processor, we see it supports Athlon 64 X2 with Dual Core technology up to 5600+ (up to 89 watt)
So we go to Wikipedia.org, and look up -> List of AMD Athlon 64 X2 Microprocessors, see which ones use the Socket AM2 processor socket, and which ones have an 89 Watt TDP, and see if there’s one that has a 2.4GHz Frequency Rate.
(Also referred to as 2400MHz, and the slang term for Frequency Rate is ‘Speed’)
http://en.wikipedia.org/wiki/List_of_AMD_Athlon_64_X2_microprocessors#Athlon_64_X2
Why yes there is. And as a matter of fact you could use a Athlon 64 X2 5600+ -> (F3), and have a Frequency Rate of 2.8GHz, plus 2MB’s of L2 cache. (Actually MORE as AMD’s are built different than Intel, who USERS seem to want to compare to. Not smart really, as they’re losing out on the stuff AMD has to offer. Intel just put’s more money into advertising, and has a bigger ‘mouth’)
Nvidia GeForce GTX280 or GTX290 series? Save your money, spend it wisely. Get an Evga GeForce GTX260 Core 216, or an XFX GeForce GTX260. Guaranteed to kick sum game booty!
Better get a power supply to run it, your stock one ain’t gonna’ do it!
Plus you better hope the GTX260 isn’t too long to fit in your computer case. I’ll bet it’ll fit, but there will be only a 1/4 inch to spare!
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01078152&lc=en&dlc=en&cc=us&product=3453790&lang=en
Juicedpc.com.au