The issue is that this system was built off of an ATi chipset that has issues when mixing high and low density components together. If you take a look at your memory modules, the module that is marked 2R will be a double sided module. The module that you purchased from Crucial is marked 1R and is single sided. As technology moves forward, higher density components are made to make higher dense modules. The lower density components are then phased out. Unfortunately, we no longer carry the lower density component modules as they are not being made anymore. To get your system to 2GB, you will need 2 1GB modules that are made up of the same component density.