If you just need a system for under $1000, take a look at my sig. The tower components (minus sound card) cost me about $900 after rebates.
My case is really awesome, I love it. It's quiet and keeps the system cool.
The XFX 7900GT is on sale right now, and they're a good company, so I would hurry up and pick up on this good deal before it's gone
The rest I'll let you pick out, but I highly recommend the parts I just listed.