4GB (1GBx4) Team High Performance Memory RAM Upgrade For Dell Dimension 9200 9200C C521 5100C Desktop. The Memory Kit comes with Life Time Warranty. at Amazon.com
New 4GB 4x1GB DDR2 PC2-5300 667MHz RAM Memory for Dell Dimension C521 at Amazon.com
4GB Memory Upgrade for Dell Dimension C521 Desktop PC 4 X 1GB DDR2 Non-ECC PC2-6400 240 pin 800MHz DIMM RAM (PARTS-QUICK Brand) at Amazon.com