Need Help Building a New Computer, $700 Budget!!!

I'm looking to build a new computer system from scratch. I will be using this system mainly for school, web-browsing, and on occasion of gaming. I would like some opinions of what you can build with the given budget of $700. I'm looking to build my system during late december or at the beginning of January so i know prices with certain components will change. Also from this build, disregard monitors, softwares, and peripherals. I would like to see what your system would look like if you had a $700 budget. Please help a fellow student out...

SAPPHIRE 100245L Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
Model #:100245L
Item #:N82E16814102770
Mail-in Rebate

$169.99 -$10.00 Instant $159.99

ASUS P5Q SE PLUS LGA 775 Intel P45 ATX Intel Motherboard - Retail
Model #: P5Q SE PLUS
Item #:N82E16813131347
Mail-in Rebate

$99.99 $99.99

Intel Core 2 Duo E7200 Wolfdale 2.53GHz LGA 775 65W Dual-Core Processor Model BX80571E7200 - Retail
Model #: BX80571E7200
Item #:N82E16819115052

$119.99 $119.99

Antec earthwatts EA500 500W ATX12V v2.0 SLI Certified CrossFire Ready 80 PLUS Certified Active PFC Power Supply - Retail
Model #: EA500
Item #:N82E16817371007

$89.99 -$40.00 Instant $49.99

Antec Three Hundred Black Steel ATX Mid Tower Computer Case - Retail
Model #:T hree Hundred
Item #:N82E16811129042

$69.95 -$20.00 Instant $49.95 -$20 combo with Earthwatts

mushkin 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model 996587 - Retail
Model #: 996587
Item #:N82E16820146731
Mail-in Rebate

$62.99 $62.99

Western Digital Caviar SE16 WD6400AAKS 640GB 7200 RPM SATA 3.0Gb/s Hard Drive - OEM
Model #: WD6400AAKS
Item #:N82E16822136218

$74.99 $74.99

LITE-ON 20X DVD±R DVD Burner with LightScribe Black SATA Model iHAS220-08 - Retail
Model #: iHAS220-08
Item #:N82E16827106265

$29.99 $29.99
Subtotal: $647.88 -$20 combo = $627.88 - MIRs if you play that game, plus shipping.

This build is a little under budget, even after shipping, especially if you count rebates (which may or may not be reliable). If you want to stretch it, or there's wiggle room, the things I'd improve first are the CPU to an e8500 or a quad, or the PSU possibly to a 610W PC Power & Cooling or 650W Antec.
If you want to lower it more, then consider what you mean by "on occasion of gaming," and lower the video card to a 4670. The forums seem to be very gamer-centric, and I suspect you'll be urged to keep the 4850, but only you know what you'll be doing. As a student, you might be downloading, listening to music, writing an assignment, gaming, and running all kinds of other background crap at the same time and would benefit more from a quad.