First time builder, starting with II X3and I need some help

The Gigabyte is a DDR2 board, but that's OK. The Asus would be the nicer board at a good price anyway.

Obviously you do not need a great deal for movies. Did you want to game at all? if so, a nice 4830 or 4670

4830
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

4670
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

If you aren't going to game at all and not overclocking, then just get this MB:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

And a 4650:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

A little confusion about ram

AM3 processors like the 720 be fit in
AM2+ motherboards that use DDR2 ram
and
AM3 mb's that need DDR3 RAM

The 3x2 gig kit you have selected is for intel triple channel ram motherboards
What you need is a 2 x2 gig kit of either ddr2 or ddr3 depending on motherboard .

IF you buy a motherboard with a 790G series mb I wouldnt bother with a graphics card . These motherboards have built in gfx chips that are way more than strong enough for video play back .

Thanks for help Outlander_04 about the ram comfusion. Here is the final build (fingers crossed).

Antec Three Hundred Case
AMD Phenom II X3 720 BE
ASUS M4A78T-E AM3 AMD 790GX HDMI ATX AMD Motherboard (won't need a video card with this one because of the 790G series mb...right?)
Western Digital Caviar Black WD1001FALS 1TB
CORSAIR CMPSU-550VX 550W
G.SKILL 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666)

I don't know about not having a video card because I do some simple video encoding from time to time. Will it matter because i was thinking of getting
SAPPHIRE 100265HDMI Radeon HD 4830 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready.

That looks good to me . That is the right mb to use without a gfx card , and its a good choice to go with ddr3/am3 as its the newer technology . ASUS have even included an HDMI port so it can be configured to send signals to a tv screen

Theres a lot of confusion about video cards and what they do . You wont have any advantage when you are encoding by using a seperate video card . Encoding is performed by the processor . Gaming gfx cards just "paint" a 3D environment of a game on to the screen.
More recently the two gfx card chip suppliers have tried to introduce technology that does use gfx card number crunching to help in repetitive encoding situations . The one that is nearest to being ready is nVidias CUDA .
http://www.nvidia.com/object/cuda_what_is.html
but so far I dont think there has been much ,if any , real world impact of these emerging technologies .

Yep. The onboard graphics of the 790GX are quite nice really. Just depends on what you need. You can even use a 780G if you want to save some:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

To Proximon,
I am so sorry for not thanking you for your first tips.
I currently have a dell 8400 with Pentium 4HT and it's dying on me now. I am finally making the push to build a PC of my own.
The ASRock M3A780GXH/128M AM3 AMD 780G HDMI ATX AMD Motherboard looks super sweet but is ASRock a reliable brand? This PC will be for some college work but it will mostly be for watching video and HD video. Considering that i intend to use it for HD video, that was reason I was considering to buy a video card. I was about to buy from Cyberpower.com but it looks like they send out the PC's a month after the order is placed.
Thanks for your tips and help. Hopefully I'll have this thing done by the end of the week.

ASRock has been getting a lot of recognition for their innovation and competitive pricing. They have been making boards for quite some time now, and are a subsidiary of Asus. Many of their products have been quite useful... I owned a board that had both AGP and PCI-E at one point, and it worked fine for about 2 years.

...And that's where I think they have had some issues. They might not hold up as long as more expensive boards, at least that seems to be the trend historically from what I've read.

So to sum up:
-Good performance
-Good to excellent features
-Good prices
-May not live as long

If it were my money I would get the Asus board and just not get a discrete graphics card until I saw a compelling reason to do so. That way I would have that crossfire option in case I had the luxury to game at some point, and a better overclock if schoolwork became more demanding.

Asrock is ASUS budget brand . The components will be slightly lower quality but those mb's work well for all but hardcore computer tuners who thrash their systems .
The 780g is not quite as strong as the 790g but is also more than you will need for video playback .
The ASRock M3A780GXH looks to be very good value

I have question about the power supply. Do either one of you think that I should scale the power down a bit or keep it at 550W?

550 is plenty, especially if you are only using Integrated graphics. If I were you I'd go for a 790g board with the 750 southbridge. Just a little more $$ with nice overclock options, and eventually you can get a nice quad core when they are good and cheap.
You could also go for a nice cheap/fast dualcore for half the price of an x3.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Eventually you could always upgrade to a quad with that motherboard

The 550VX is an excellent PSU. It is more power than your current plans involve but then you never know what might happen. You could go with an LS-450 from BFG or a Corsair 450VX if you wanted to cut costs.

I am sorry but that CPU recommendation would have to be used in an AM2(+) motherboard. It will only work with DDR2 memory, so in ones with only DDR3 memory(AM3) that CPU wouldn't function. My bad but my recommendation still stands.

Well it seems that i am def. ready to start. Thanks for your recommendation doormatderek. I appreciate it.
One more thing, do I stick with the stock heatsink or upgrade. i do intend to do some video encoding but nothing that could be considered pro stuff.

This is the final, give me your opinions

Antec Three Hundred Case (to save money i could reuse my Dell8400 midtower)
AMD Phenom II X3 720 BE
ASRock M3A780GXH/128M AM3 AMD 780G HDMI ATX AMD Motherboard
Western Digital Caviar Black WD1001FALS 1TB
CORSAIR CMPSU-550VX 550W
G.SKILL 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666)
Samsung SH 222A

Should I get a heatsink or stay with the stock heatsink?

You'll need one to overclock, but at stock speeds you should be OK.

That build looks great. As proximon said if you plan to overclock then you will need one but otherwise the stock cooler will do the job! Good luck with the build.