For this you will need to get one of the xeon 771 socket cpu like Xeon e5472 for 1600 fsb mobos, or e5430 kind of cpu for 1333, also it would be great to get ddr3 775 socket mb also.. at the moment I have 2 Desktops running e5472 and e5430 with gigabyte mb’s. You can see what you need to do with your mb, how to modify socket so you can get your xeon with sticker mod in it to get quad core cpu with great performance to boost your old rig.
Also you can find cheap cpu’s with stickers on ebay for a nice price.. And if you can get an ssd drive in that rig you’l get awesome performance..
My specs for this:
CPU: Intel Xeon 5472 3.0 Ghz 12 Mb cache
MB: Gigabyte GA-EP43T-S3L Intel P43 Express DDR3 Socket LGA 775 Motherboard
RAM: Crucial Ballistix Sport 8GB Kit 4GB x2 DDR3 1600 MHz PC3-12800 CL9 1.5V
HDD: SSD 120GB 120G Kingston SSDnow V300 Solid-State Hard Drive
VGA: Vamery CPU 2GB 256Bit DDR3 GTX650 PCI Express 3.0×16 28nm HDMI VGA Graphics Card
|Xeons that are compatible with each chipset|
|Chipset||5xxx Series||3xxx Series||45nm||65nm|
|P45, P43, P35, P31, P965
G45, G43, G41, G35, G33, G31
nForce 790i, 780i, 740i, 630i
GeForce 9400, 9300
|Q45, Q43, Q35, Q33
|nForce 680i and 650i||Yes||Yes||Maybe||Yes|
Also you can check this link for images and tutorial HOW to do this.