New gaming build - Seeking advice on my choices (~700$ Can)

Purchase Date: I'd like to get it as soon as possible. If waiting a couple months is the smartest thing to do, I'll consider that too.
Usage from most to least important: Gaming (WoW mostly, SC2 and D3 when they're out, some RTS as well), watching some movies, general usage.
Parts not required: I have a monitor, mouse, I can dig up a keyboard, or I might have to buy one, speakers laying around somewhere, I'll be buying Vista 64-bit.
Preferred website for parts: Infonec.ca or another Canadian site that offers pick up in the Toronto, GTA area, or one with free shipping.
Overclocking: Maybe - I don't know much about it, I'm open to learn if it will really save me money/improve performance.
Crossfire: Maybe - I'd like to have the option of upgrading to a Xfire config, unless it means I need to invest a lot more in a better CPU or other components to avoid bottlenecking.
Monitor: I will be using a 22-inch HP monitor.
Other: I want to build something that's going to last me a bit, with upgrade options if possible. However, I'm conflicted, is it better to future proof and spend more or buy cheaper now, and replace with cheaper later? I'm looking for a bit of education on this if possible.

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1 436944 SH-S223F/BEBN Samsung SH-S223F 22x DVD±RW Drive $27.99
http://www.infonec.ca/site/main.ph [...] &id=436944

1 353551 OCZ2P10664GK OCZ DDR2 4GB (2x2048) D/C Kit PN - OCZ2P10664GK PC2-8500 Platinum 4GB Edition Dual Channel $59.00
http://www.infonec.ca/site/main.ph [...] &id=353551

1 353163 THREEHUNDRED Antec THREEHUNDRED Small Versatile Case Black finish $59.00
http://www.infonec.ca/site/main.ph [...] &id=353163

1 436948 ST3320613AS/418AS Seagate Barracuda 7200.11 - Hard drive - 320 GB - internal - 3.5" - SATA-300 - 7200 rpm - buffer: 16 MB $53.50
http://www.infonec.ca/site/main.ph [...] &id=436948

1 316322 EA500 Antec EarthWatts EA 500 - Power supply ( internal ) - ATX12V 2.2 - AC 100-240 V - 500 Watt - active PFC $79.99
http://www.infonec.ca/site/main.ph [...] &id=316322

1 410466 Sapphire 4870 Sapphire HD 4870 512M GDDR5 2XDVI+VO PCIe (RL) $149.99
http://www.infonec.ca/site/main.ph [...] &id=410466

1 443049 M4A78-E ASUS M4A78-E SKT.AM3 AMD 790GX/SB750 2PCI/2PCI-E X16, 4D.DDR2-1066, RADEON HD3300 GPU,HDMI,ATX $125.00
http://www.infonec.ca/site/main.ph [...] &id=443049

1 443136 HDZ720WFGIBOX AMD Black Edition - Processor - 1 x AMD Phenom II X3 720 / 2.8 GHz - Socket AM3 - L3 6 MB - Box $155.00
http://www.infonec.ca/site/main.ph [...] &id=443136

Total: $709.47

I'd like to save as much money as possible, if I can accomplish what I'm after for less, please let me know. Additionally though, if I can make some major upgrades for a minor cost difference, I'm interested in those suggestions as well (who isn't though?).

To the best of my knowledge, everything in the list should work together, but I don't consider myself extremely knowledgeable with these things, so please let me know what is/isn't compatible if anything.

Thanks in advance, I really appreciate any constructive input anyone has.

I really wouldnt suggest you get the .11's on seagate. Firmware problems went sky high and brick problems on the terabytes hit the fan. the .12's are probably listed as a fast hdd but, during other processes they either didn't do so well or they did alright.

I would go with wd black / samsung f1 - f2.

The board you listed is actually the AM2+ board so it will work with DDR2, the M4A78T-E is the AM3 board and only works with DDR3 and AM3 CPUs.

Definitely dont get the seagate 11 series, see about getting a 500GB seagate 12 series of samsung F3 drive, they are both single platter drives and will be fast and quiet.

asus and gigabyte both differentiate the AM3 boards by adding a T onto the end of the model, its because the boards are identical except for DDR3 slots instead of DDR2 and an AM3 socket instead of AM2+, all of the other components are the same.

get a wd hdd