|riider is correct in what he has posted above. You probably have a 512MB module currently installed. there is no 518MB. |
This is an excerpt from the link below.
533-MHz and 667-MHz ECC and non-ECC DDR2 SDRAM
NOTE: Ensure that you do not mix ECC and non-ECC memory.
Your specs state you are using 32 bit Windows so 4GB is the max. Use 2- 2 GB sticks. Remove the 512MB. Get the same speed and latency as installed if possible.
Use the crucial.com online scan to determine what you have and what can work.