Is this a good mid-range gaming computer build?

[Itslukelol]

Okay, so about to buy a new computer. and thanks to thehelp of all the amazing people on this site i think i am finally done. I just wanted one last critique. So here is the hardware. I am going to be gaming on it. games like WoW, Starcraft 2, Diablo 3 ect.

-Seagate Barracuda 7200.11 ST3500320AS 500GB 7200 RPM SATA 3.0Gb/s Hard Drive ($64.99)

-ASRock A780GXE/128M AM2+/AM2 AMD 780G ATX AMD Motherboard - Retail (79.99)

-APEVIA ATX-CW500WP4 500W ATX Power Supply - (39.99 before 10 dollar mail in rebate)

-G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory Model F2-8500CL5D-4GBPK (54.99)

-AMD Athlon 64 X2 7750 Kuma 2.7GHz Socket AM2+ 95W Dual-Core black edition Processor Model AD775ZWCGHBOX (63.50)

-MSI R4830-T2D1G OC Radeon HD 4830 1GB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card (139.99 before 30 dollar mail in rebate)

I am thinking the only thing that i could change is the RAM.

i have 450 to spend...with this build it is exactly 450 bucks.

I am running Windows XP 32 bit so idk if 4gigs is necessary.

thanks for all the help.
I am using the case and optical from my old computer...

its just a basic case and CD/DVD RW