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Will My Mac (iMac5,1) Work with one 2gb stick of Ram and one 1gb stick, or do I have to cave in and buy two 2gb Sticks, only to be able to access 3gb?

The maximum memory in your machine is 3 GB. Is is not installed in pairs. Your 2GB & 1 GB sticks should work fine together. Supports 667 MHz PC2-5300 DDR2 SDRAM Here’s a guide on it: http://www.everymac.com/systems/apple/iM