Gateway PC, Core 2 Quad 2.33GHz Quad-Core CPU / 4GB / 640GB for $409.99 after applying coupon code PAYPAL20 and using PayPal checkout to take $20 off $100.  Here is a screenshot for your reference.  This system features an Intel Core 2 Quad (quad-core) 2.33GHz Q8200 CPU, 4GB of DDR3 RAM, 6400GB drive, 16x DVD burner, Gigabit Ethernet, eSATA, USB, HDMI video output, Windows Vista Premium 64-bit, and more.  Note that it is also eligible for Free Windows 7 Upgrade.
This deal has expired as the coupon has bee pulled.  Congratulations to those able to get in on it.