I've pasted links to the DELL support site. On this web page under upgrades you'll find a link "Upgrades, Parts & Accessories" which gets you to a list of all their models. I'm a little confused thou because the Optiplex model number you listed does not exist. Your office pc model, however is listed and I followed the link and it states that you have DDR400 memory in the system. You will be able to upgrade to 2x 512MB or 2x 1GB memory sticks for a total of 1GB or 2GB system memory. For the Optiplex model (if the correct model number is GX240) you can buy 2x 512M memory sticks. This is SDR133 memory, however. Dell lists you prices if you want to get it from them (the higher priced model is with ECC support, which for home use you certainly don't need).
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