Sorry, forget about our earlier recommendations. Here's what I have found:-
Intel® Desktop Board D945GCNL — System memory for D945GCNL
System Memory Features
The board has two DIMM sockets and supports the following memory features:
- 1.8 V (only) DDR2 SDRAM DIMMs with gold-plated contacts
- Unbuffered, single-sided or double-sided DIMMs with the following restriction: double-sided DIMMs with x16 organization are not supported
- 2 GB maximum total system memory
- Minimum total system memory: 128 MB
- Non-ECC DIMMs
- Serial Presence Detect
- DDR2 667, DDR2 533 or DDR2 400 MHz SDRAM DIMMs
So your best bet is 2 dimms of 1gb. As you already have a dimm of DDR2 667, add another.
EDIT:-
Ok its already been posted. Thanks d3p5kor.