What is the maximum supported RAM size and frequency?
If I already have 1GB DDR2 could I still increase my RAM memory?
See http://www.intel.com/support/motherboards/desktop/d946gzis/sb/CS-026621.htm. For your configuration, it'll be 4GB abd 667MHz. I assume you have you have two 512MB DIMMs, so you can add another two 512MB or 1GB DIMMs.