I have now run the MS Memory Tester and Memtest and Memtest86 (as Carol suggested), and it's finding no problems at all. I switched the memory sticks over, but the problem persists - I'll follow your lead and take both out next, Mouser, and then replace. When I ran Everest, I noticed that there seems to be a difference between the modules, as you'll see below (sorry for including this in the post, since it's pretty long and bulky). This info means little to me - but does anything leap out at a more savvy reader?
[ DIMM1: Micron Tech. 8VDDT3264HDG-335C3 ]
Memory Module Properties:
Module Name Micron Tech. 8VDDT3264HDG-335C3
Serial Number 111DB16Eh
Manufacture Date Week 41 / 2003
Module Size 256 MB (2 rows, 4 banks)
Module Type Unbuffered
Memory Type DDR SDRAM
Memory Speed PC2700 (166 MHz)
Module Width 64 bit
Module Voltage SSTL 2.5
Error Detection Method None
Refresh Rate Reduced (7.8 us), Self-Refresh
Memory Timings:
@ 166 MHz 2.5-3-3-7 (CL-RCD-RP-RAS)
@ 133 MHz 2.0-3-3-6 (CL-RCD-RP-RAS)
Memory Module Features:
Early RAS# Precharge Supported
Auto-Precharge Not Supported
Precharge All Not Supported
Write1/Read Burst Not Supported
Buffered Address/Control Inputs Not Supported
Registered Address/Control Inputs Not Supported
On-Card PLL (Clock) Not Supported
Buffered DQMB Inputs Not Supported
Registered DQMB Inputs Not Supported
Differential Clock Input Supported
Redundant Row Address Not Supported
Memory Module Manufacturer:
Company Name Micron Technology, Inc.
Product Information
http://www.micron.co...egory.jsp?path=/DRAM [ DIMM3: Kingston K ]
Memory Module Properties:
Module Name Kingston K
Serial Number 18FFFFFFh
Manufacture Date Week 29 / 2004
Module Size 512 MB (2 rows, 4 banks)
Module Type Unbuffered
Memory Type DDR SDRAM
Memory Speed PC2700 (166 MHz)
Module Width 64 bit
Module Voltage SSTL 2.5
Error Detection Method None
Refresh Rate Reduced (7.8 us), Self-Refresh
Memory Timings:
@ 166 MHz 2.5-3-3-7 (CL-RCD-RP-RAS)
@ 133 MHz 2.0-3-3-6 (CL-RCD-RP-RAS)
Memory Module Features:
Early RAS# Precharge Not Supported
Auto-Precharge Not Supported
Precharge All Not Supported
Write1/Read Burst Not Supported
Buffered Address/Control Inputs Not Supported
Registered Address/Control Inputs Not Supported
On-Card PLL (Clock) Not Supported
Buffered DQMB Inputs Not Supported
Registered DQMB Inputs Not Supported
Differential Clock Input Supported
Redundant Row Address Not Supported
Memory Module Manufacturer:
Company Name Kingston Technology Company, Inc.
Product Information
http://www.kingston....products/default.asp