Need advice on very low budget web browsing/gaming pc

Approximate Purchase Date: Within one or two months of April 2011

Budget Range: Preferably $300-$400; Realistically up to $500 before rebates

System Usage from Most to Least Important: Light/medium gaming, e.g. minecraft on 'High' settings with extensive mod use and possibly coop fps such as L4D (1) and borderlands. Next in line is Web browsing, probably least important is watching low/med quality movies/videos (youtube mainly)

Parts Not Required: keyboard, mouse, speakers, optical drive, monitor (though I will probably upgrade to a cheap lcd monitor at some point so recommendations are welcome, but not expected)

Preferred Website(s) for Parts: newegg, amazon, sites that would be considered trustworthy by a careful purchaser

Country of Origin: U.S. of A.

Parts Preferences: I have a listing, but I don't know how compatible they are, And really I know very little about parts/manufacturers, etc.

Overclocking: possible, but I barely know what overclocking is so not needed.

SLI or Crossfire: highly doubtful

Monitor Resolution: big old square monitor, 1024x768? And an lcd monitor thats one the fritz. But basically a low end resolution

Additional Comments: Loud or ugly matters not.

I am mostly looking for High FPS on Minecraft on Normal/high settings (far and fancy) and able to play L4D and Borderlands (and similar) with good/acceptable Framerate on normal/low settings.

Here is what I've found for myself.

AMD Athlon II X2 250 Regor 3.0GHz 2 x 1MB L2 Cache Socket AM3 65W Dual-Core Desktop Processor ADX250OCGMBOX

GIGABYTE GA-MA78LMT-S2 AM3 AMD 760G Micro ATX AMD Motherboard

HIS H467QR1GH Radeon HD 4670 1GB 128-bit DDR3 PCI Express 2.0 x16 HDCP Ready CrossFireX Support Video Card

Antec EarthWatts Green EA-430D Green 430W Continuous power ATX12V v2.3 / EPS 12V 80 PLUS BRONZE Certified Active PFC Power Supply

G.SKILL 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600) Dual Channel Kit Desktop Memory Model F3-10600CL9D-4GBNT

Western Digital Caviar Blue WD3200AAJS 320GB 7200 RPM 8MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive

RAIDMAX Tornado ATX-238WY Black SECC Steel ATX Mid Tower Computer Case

I'm a bit iffy on the possibility of having gone overkill on the PSU (not that a safe and good PSU is ever a bad idea). But anything cheaper that still wont let my computer melt/surge? will do.

And if anyone could point me to a cheap windows xp I would appreciate it.

Oh, and I have absolutely no intention of playing Crysis or Crysis 2 or BF2 or CoD4 etc. I have a PS3 for that (as my twitch reflexes with a mouse are lacking).

I am aiming for decent visuals on older(ish) games and mostly care about a good steady 40-60 FPS.

Thanks for any help!