First, to answer your 2 questions:
1) This processor (Intel Xeon 5320 - both L and E) are 64-Bit Quad Core Xeon processors.
Check details for each of the 6 variants: Intel Xeon E/L 5320
2) Intel® EM64T requires a computer system with a processor, chipset, BIOS, operating system, device drivers and applications enabled for Intel EM64T. Processor will not operate (including 32-bit operation) without an Intel EM64T-enabled BIOS. Performance will vary depending on your hardware and software configurations. See http://www.intel.com/info/em64t for more information.
So this tells you that a 64-Bit processor will not work on a 32-bit enabled motherboard that does not support 64-bit processor.
Now as for your other concerns/questions;
Microsoft SBS 2003 R2 (Standard/Premium Edition) supports 4GB memory (RAM) at max, tested and verified. This could be the reason that your OS is only registering 4GB at max. See the system requirements for SBS 2003 R2 for yourself.
Moreover do confirm that the upgraded memory is of the same type / model as the previously installed memory and that motherboard support for max memory.
For more information on hardware support for SBS 2003:
As for 64-bit version of SBS 2003, you should install it and also update us on your findings however if Microsoft does not allow SBS 2003 64-bit Ed to support over 4GB memory, I am not sure there's much you can do lest there is a workaround for that.
For any further query, feel free to contact us.
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