Building a computer is like meccano, just put the parts in the place that it fits, putting force where it is required (inserting ram) and be very light when putting the CPU in.
$1500 is a nice chunk of money, so you will get some great parts in it, I will not say get this, but will give you a guide on what is good.
You want to spend the most money on the videocard, as this is where you get most of the performance gain, but not to skimp on other parts so the system isn't bottlenecked. The AMD X2 will fit nicely in that budget, and will ensure you have good performance in future games, but the M2 socket is due to be released soon, so wait for that.
The graphics card is very important in games, chose a good one. The Nvidia 7800gt and GTX are very good, but the GTX doesn't offer as much performance for the extra money. With ATI cards, stick with the higher up numbers, as their cheaper cards are not as good price:Performance wise. ATI does not preduce very good drivers, but their new card X1900XTX perfroms extremly well when there is AA, soft shadows and AF, as it can now render the image 3 times, once for AA, once for AF and once for HDR, in the same cycle, where as nvidia will have to render the image 3 times, but nvidias cards have more pipelines (not unified) This is shown here: http://www.anandtech.com/video/showdoc.aspx?i=2679&p=12
Dual video cards do not offer good performance for twice the money,
For memory, 2gb's is starting to be required, as FEAR and BF2 are using more than 1gb. 2x 1gb sticks is better than 4x 512. Always go in pairs for ram to get dual channel.
For AMD Asus, DFI and MSI are the top brands. For Intel Asus is the best out there.
Seagate comes out best for hard drives, in my experience.
Always go for a premium PSU, as the cheap ones die, and take out hardware.