CPU Upgrade (dual core to six core)

I'm currently beginning a project of completely rebuilding my dell Inspiron Desktop 546MT.
i am very new to the cpu upgrades. i have quite few knowledge about graphic cards, but empty minded on mobos, cpus, psu.. etc i want to completely work on this on my own, im more like a do it yourself type of person. okay lets get to the business, so far the only upgrade i done to my desktop is the graphic card, and psu, both upgrades went quite well. so next in line for me would be the processor, then upgrade from Vista Home Basic 32bit to Windows 7 Ultimate 64 bit, then probably a few more rams (i don't need help on, its as easy as tying your shoelaces ), and most likely add a few monitors (i dont need help on it either, like i said i a few knowledge on video cards, so it shouldn't be bad) so ugh, to sum it all up, i need a few advice on upgrading my current processor (AMD Dual Core) into a more powerful and stronger processor.

According to my research:
i just need the processor that fits my mobos socket ( AM3), a heatsink that can cool 125watts of power, and a psu that can handle the 6 core processor. so i decided to go ahead and purchase an AMD Phenom II X6 2.8ghz (http://www.newegg.com/Product/Produc...82E16819103851) which comes with a certified heatsink, and Corsair 600w PSU (http://www.newegg.com/Product/Produc...82E16817139019). so i think i need everything i need. thats why i need you the people of tech support, to give me a few advices on working on this. i will post my current projects, i will also edit this topic when my upgrades went successful. WISH ME LUCK!

Base on CPU-Z heres my current infos:
PSU: Antec 400W

OS: Windows Vista Home Basic 32bit (will upgrade to 7 Ultimate 64bit, after processor)
Processor: AMD Athlon II X2 215 ( will upgrade to AMD Phenom II X6 1055T)
Core Name: Regor
Socket: AM3
Technology: 45nm
Core Voltage: 0.992v
Core Clock Speed: 800Mhz
Bus Speed: 200Mhz

Motherboard:
Manufacturer: Dell Inc.
Model: 0F896N AO2
Chipset: AMD 780G
Southbridge: AMD SB700
BIOS: Dell Inc A10

Memory:
Dual DDR2 1024mb (total 2048mb)

Graphics:
PCI-Express x16
DDR 3 ATI Radeon HD 5550 1024mb ( cheap i know) ( upgraded from DDR 2ATI Radeon HD 3450 256mb) ( will still be upgraded soon when i get more PSU power)

so can anyone give me some advices?