Memory Type DDR SDRAM
Number of Memory Slots 3 x DIMMs
Supported RAM speeds 333 MHz • 266 MHz • 200 MHz
Max Supported RAM 3 GB
These are the supported RAM speeds. It should be noted that the maximum supported RAM of 3 GB would be at the lowest speed of 200 MHz, the faster the speed, the less the maximum total will be. I think the 1Gb you installed takes you over the maximum for the speed you are using, you will need to check your mobo manual to find the exact combination of spedd and maximum installation.