According to the manual, your 350 should accept 256mb ecc registered dimms that you have.  Does the system post if you have just one dimm installed??  Does it post if you reinstall the original dimm?? 

post beeps

1  BIOS checksum failure; the memory refresh circuitry on the system board is faulty

2  Parity error; faulty DIMMs or defective system board

3  Base 128 KB memory failure

4  Timer not operational

5  Processor error

6  8042 - Gate A20 failure

7  Processor exception interrupt

8  Display memory read-write error

9  ROM checksum error-  This error usually requires that you replace the BIOS firmware.

10  CMOS shutdown register read/write error

11  Cache memory bad

this is according to the manual  http://support.dell.com/support/edocs/systems/spe350/en/index.htm

If it posts fine with the original ram, then i would try and update the bios and then retry your ram.

Hope this helps.

Thank you for the reply. My server would not boot with all four DIMMs installed, or with only a single DIMM installed. It does runs correctly with the original DIMM installed.

My PowerEdge 350 machine currently has:
http://www.micron.com/products/partdetail?part=MT9LSDT1672G-133

I believed the only 256MB memory module from Micron that will work are:
http://www.micron.com/products/partdetail?part=MT9LSDT3272G-133

Thanks again for your information, and if I purchase the MT9LSDT3272G-133 modules I let everyone know how it goes.

Note: As a test I installed the memory modules in a PowerEdge 2450 and that machine recognized the memory fine.

Rod