It depends.  What speed is it?  What size?  What rank?  It would be easiest to go here and post your Original Configuration here (enter your Service Tag, then go to the System Configuration tab, Components): www.dell.com/.../ProductSelector Or you can start here: www.xbyte.com/Dell-PowerEdge-2900-Memory.aspx
I have a DELL PowerEdge 2900 which is sending me this alert through OpenManage:  Message:Alert message ID: 2321, Controller error. Single-bit ECC error. The controller DIMM is nonfunctional. There will be no further reporting., system, Controller 1 (PERC 5/i Integrated). Can someone provide the correct part number for the DIMM module referenced ? (not the server RAM memory DIMM). Unit is no longer under a service contract. Thank you !  
DIMM Part Number Needed - Please