The processor will have to be the exact same as the one you already have in there.

You need to have exact matches - chances are by now, in order to upgrade, you'll need to buy two identical CPUs - unless you can find one identical to the one you had (and that will probably wind up leading you to the used-CPU market).

So are the steppings different in the two I listed? When I look up the CPU info on linux it says that the current stepping is 11, while the ones that you can purchase with the exact same model number says the stepping is B3. 

I would think that I could just install two of these, same wattage, same socket.. right?

http://www.newegg.com/Product/Product.aspx?Item=N82E16819117151

Thanks for the help guys.... but I think part of my question is misunderstood. When I run procinfo it shows stepping is 11. this command always shows an integer value for the stepping, but a number like intel advertises. If I convert the 11 to hex, I get the B, but don't know where the 3 comes from.... 

I think that what shows in procinfo as 11 is in fact the B3 stepping, but I can't figure this out for sure. 

I don't believe the Poweredge 1900 can support any of the 45nm Xeons (5200 and 5400 series). You'll need to look for a Xeon in the 5300 series (for Quad core) or 5100 series (for dual core).

Google CPU-Z. Run this on the server and it should tell you exactly which stepping your processor is.

CPU-Z is windows only. I am runing RHEL. 

Ok, just as an update, I checked this BIOS release notes and it shows that my version supports mixed steppings between B3 and G0 so it doesn't really matter.

http://ftp1.us.dell.com/bios/pe1900-020500BIOS.txt