Someone to show me the way

Hello my new friends.
i have an old PC (Kudoz 7x, Athlon XP 2100+ 1.733MHz, 1Gb ram, NVidia GeForce FX 5700 LE 128 MB, Windows XP Professional version 2002 SP2) and two children 15 & 12 yrs.
As you can understand they can't play many games and here comes my trouble.
I bought a GIGABYTE GA-M720-US3, KINGSTON KHX8500D2/2G DDR2 2GB PC8500 1066MHZ HYPERX, ASUS EN9600GSO CUDA MAGIC/HTDP 512MB PCI-E RETAIL and a WESTERN DIGITAL 500GB WD5002ABYS RE3 SATA2.
My question is: wich processor should i buy? The AMD Athlon X2 Dual-Core 7750 Black Edition (AD775ZWCGHBOX) or the AMD PHENOM X3 8600 2.3GHZ TRIPLE-CORE TRAY??
Mostly will be used for gaming and home apps.
Thanks for your forbearance and for your help.

get any newer am3 chip cuz your mother boards supports it http://www.gigabyte.com.tw/Product [...] A-M720-US3

Need a range on the amount of money you would like to spend.

A 9600gso should not require a super-duper CPU - the Athlon II x2 245 Regor is $66 at The Egg.

The new Athlon II x4 Propus will be here next week. The initial procs will be Deneb-based but I doubt you will be able to unlock with an nVidia chipset.

wisecracker: about 70 Euro (aprox. 95 USD)

From Scan UK

AII x2 540 ----> PhII x2 550BE: £45 to £76 including VAT

The PhII 545 is £66.30.