Updating MB/Processor/Memory OpSys

I am running the following configuration on a desktop about 3 years old, and would like to update the processor to an Intel i7, new MB, 64-bit Windows Pro, and either 16-32Gb of memory. I would like to keep the cost below $400, excluding the operating system, and appreciate any suggestions.


HP M9000 series
Intel Core 2 Quad CPU Q9300 @ 2.5GHz
RAM 4GB DDR2 SDRAM
Motherboard Pegatron Benicia
Graphics ATI Radeon HD 5700 Series
Drive 0 Samsung 256GB SSD SATA
Drive 1 Seagate 3TB SATA ST3000DM001-1CH166
USB 2.0 – 6 port
Gigabit Ethernet, USB Wireless 802.11 b/g Adaptor
No Bluetooth
Windows 7 Professional 32-bit

-rperkins