First, your system will probably have to be a 2800 II.  The 2850 had a II revision, but I don't know if the 2800 did.  It will have a II in a circle in the upper-left corner of the front chassis plate, and OMSA may show the revision in the System Information screen. Second, your part number will be "somewhere" on the motherboard, as something like XX-0YT224-XX....., where YT224 is the actual part number.
I have an old (2006) Poweredge 2800 server with one Xeon single core 64 bit processor in it. I have heard that my motherboard may be compatible with the dual core Xeons (Paxville) and would like to take advantage of this. I see that only some of the motherboards which came with the 2800 are dual-core compliant.  Before I make a purchase I would like to confirm that my motherboard is compatible with the Paxville CPUs. Where is the part number / model number of my motherboard? The sticker on the board states that it is an A04 version. I assume this is the BIOS rev. and I will be flashing A07 today. The Changelog of the BIOS update states that they added dual-core support in A04. I can supply pictures if you need. Thanks for your help.
Which Motherboard do I have? Poweredge 2800 server.