Trying to build first gaming computer

Hi, I'm trying to building a good gaming computer and but don't really know what to get at all! So please help!

APPROXIMATE PURCHASE DATE: Within the next month

BUDGET RANGE: $800-$1000

SYSTEM
USAGE FROM MOST TO LEAST IMPORTANT: Gaming-Movies

PARTS NOT REQUIRED: Keyboard, Mouse, Speakers, Monitors

PREFERRED WEBSITE(S) FOR PARTS: any

PARTS PREFERENCES: Something that will run Left 4 Dead ( and all new recent games) Smoothly and without problems

OVERCLOCKING: Maybe

ADDITIONAL COMMENTS: I don't really know much on building a gaming pc or a pc period ( which is why I'm posting here)

Smithereen has a good build there. I've gone in a slightly different direction, building a solid platform to expand on.

AMD X4 940
This has a nice price, but it's not a DDR3 compatible CPU, sadly. It's a step up in speed from the X3 720 though.

ASUS M4A78-E AM2+/AM3 AMD 790GX
Good crossfire board. Will probably be in combo with this CPU shortly. Newegg has the wrong board listed at the moment, and I alerted them.

G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066
You want 1066, lowish price, CAS 5, and lowish voltage. Oh, and a low profile. No raised RAM heatsinks on AMD boards as the RAM is close to the CPU and cooler.

Scythe Shuriken CPU cooler
This top-down cooler should fit the board well, and do a decent job. I'm trying to research large coolers with these AMD boards now... there are issues.
Thermal paste

Cooler Master HAF A good case that will last a long time. Excellent cooling and ease of use. Nice features.

PC Power & Cooling S75QB 750W
Not the red one, which would save you 10 bucks

Saphire 4870 1GB
You can add a second if you need it later.

Wd 640GB Caviar Black
Fast. Lot's of room for a gamer.
HP retail DVD burner


$981 before rebates, combos, and shipping

Thanks for all your help guys!

The first build you posted.