With your budget, you can do very well. Here are some of my ideas:
1) The 2500K is the cpu of choice for gamers. 4 cores is more than you need, and it will overclock easily past 4.0. That is what the"K" is built for. About $200. Less if you can pick one up at a microcenter.
2) The graphics card is the real engine for gaming. Spend your budget here. Something like a GTX560 or 6870 will be about $150. If you have the budget, go higher up to a GTX570 or 6970 for gaming.
3) Get a Z68 motherboard. That will allow you the ability to use the integrated graphics of the 2500K to aid in video editing. I am no expert there, do some research on "quick sync" You might look at micro-ATX motherboards which have only 4 expansion slots. They are cheaper, but will not run multiple graphics cards well.
4) 8gb of ram is a good number, get a 2 x 4gb kit. Speed specs are unimportant. Don't pay extra for high speeds or fancy heat spreaders. DDR31600 is about as high as you need to go.
5) Your case makes me smile! I am not much of a fan of "bling". I think the case should be replaced. It has only two 80mm fans for cooling. That is not enough to cool a good graphics card. Look for a case with tow 120mm intake fans, or equivalent. You can get a Antec 200 for $30:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Antec 300 illusion model is a good value for $70:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
For the quietest case around, look for the Antec SOLO2 at $130:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
The case I use is a silverstone TJ08B-E which is a micro-atx case for $99.
It has a 180mm intake fan, and is very quiet and cools a GTX580 based system very well.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
6) A psu of 600w will power any card up to a GTX580. Just get a quality unit. My short list of quality units would include Corsair, PC P&C, Antec, Seasonic, and XFX. Your currrent psu is a cheap 450w unit with only 18a, not enough for today's gaming systems. Here is a list of what some graphics cards require:
GTX550ti needs 400w with 24a on the 12v rails plus one 6-pin PCI-E power lead.
GTX560 needs 450w with 24a on the 12v rails plus two 6-pin PCI-E power leads.
GTX560Ti needs 500w with 30a on the 12v rails plus two 6-pin PCI-E power leads.
GTX570 needs 550w with 38a on the 12v rails plus two 6-pin PCI-E power leads.
GTX580 needs 600w with 42a on the 12v rails plus one 6-pin and one 8-pin PCI-E power lead.
GTX590 needs 700w with 50a on the 12v rails plus two 8-pin PCI-E power leads or 4 6-pin power leads.
7) You probably want to get a DVD burner. They are only about $20. I have used Samsung and ASUS which are ok.
8) At 1024 x 768, you do not need the strongest graphics card. But, consider adding a 22-24" 1080P monitor. You will see more of your game and have more desktop real estate for other uses. Do keep your old monitor if you have the desk space. I find it useful to keep e-mail and monitors open while gaming. It adds no appreciable load to the gaming card.
9) Windows-7 home premium 64 bit is the os of choice.
10) Plan for an aftermarket cooler. It will keep your pc quieter under load, and will let you OC higher and easier. No need to pay much. $30 gets you a CM hyper212 or a Xigmatek gaia cooler. Paying more gets you only marginal improvements.
Whatever you do, good luck---