$1200 Desktop first time help

First time building a computer. This is what I have done so far. From what I've read it seems that the CPU and motherboard dictate how the rest of the computer is made. I'm not sure which of these CPU's below are best for what I need. I now have to read up on graphics cards. Any help is greatly appreciated.


APPROXIMATE PURCHASE DATE: Next Friday 9/17/10 at the latest.

BUDGET RANGE: $900-$1200 Before Rebates

SYSTEM USAGE FROM MOST TO LEAST IMPORTANT: The computer will be use for games, and school work which could include a bit of coding in Matlab.

PARTS NOT REQUIRED: The only part not required is the mouse.

PREFERRED WEBSITE(S) FOR PARTS: Website doesn't matter to me.

COUNTRY OF ORIGIN: USA

PARTS PREFERENCES: No Real preferences though my choices are lean towards AMD.

OVERCLOCKING: Maybe

SLI OR CROSSFIRE: Yes

MONITOR RESOLUTION: Not sure about this yet.

ADDITIONAL COMMENTS: I made my budget bigger than I initial wanted it to be due to the lack of monitor and most peripherals.

CPU

AMD Phenom II X3 740 Black Edition Heka 3.0GHz Socket AM3 95W Triple-Core Desktop
$88.99

Needs Heat Sink ARCTIC COOLING Freezer 64 Pro 92mm Ceramic CPU Cooler
$29.99
$118.98

AMD Phenom II X4 955 BE 3.2GHz
$154.99

AMD Athlon II x3 440
$74.99

Motherboard
ASRock 880G EXTREME3 AM3 AMD 880G
$109.99

ASRock 770 EXTREME3 AM3 AMD 770
$79.99