Quad Core price drop on July 22nd you can get it for 299$ , but its B3 stepping , You want G0 so you can OC it to like 3.6. If you dont plan to OC then it doesnt matter for you.
Get a 680I Mobo 150$
4gb RAM DDR (its 50$ a peice)= 200$
Keep ur Old HD
Get Some liquid cooling (will be expensive, research them) dont buy a cheap one.
Get Gforce 8800