(Redirected) Dell 690 Workstation upgrade options

I have a Dell 690 workstation with 2 dual core Xeon processors.  I would like to know what my options are for upgrading to quad core?  Ideally something over 2.4GHz and hyper-threaded.  Currently I have:

2.00 gigahertz Intel Xeon 5130 

64 kilobyte 

primary memory cache 4096 kilobyte 

secondary memory cache 64­bit ready 

Multi­core (2 total) Not hyper­threaded

Board: Dell Inc. 0MY171 A02 

Serial Number: ..[Admin note, serial number removed per TOU.] TD

Bus Clock: 1333 megahertz BIOS: Dell Inc. A08 04/25/2008

Any info / part numbers would be appreciated.  Thanks!