[johnross2007]

The only incompatibilty really is if you have a mobo that supports DDR2-800 but your RAM is DDR2-1066. That RAM will still work but might get underclocked to 800.

In the future I would suggest never buying some parts before others unless you are getting some deal on those parts. Builds often change in the last few days when you find deals that weren't there before.

I don't think Crossfire and SLI is worth it. The only good reason I could see for getting a mobo capable of it is in case you want to buy he exact same GPU a year or two down the line when its cheaper. But getting a new card to replace the old is still usually more cost effective.

For graphics I would go with the 9800GT but I am an unabashed Nvidia fanboy so take that with a grain of salt .

For a case get whatever you like the best. From what I hear the Antec 900 lacks filters on the front fans, but those are easily bought and installed and will help keep dust out of your computer. I wouldn't let that affect your decision, just something you might want to do should you pick the antec 900.

edit: Do you plan on overclocking?