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I bought two sticks of this RAM http://eshop.macsales.com/item/Other World Computing/3200DDR1024/ and put it in my Dual G5, following these instructions http://www.info.apple.com/usen/cip/pdf/g5/memory_c.pdf , but when I go to 'ABout this Mac,' it doesn't recognize that I've added RAM. I put the two sticks in slots 3 and 4 of the bottom half. Did I do something wrong?

You need to put the RAM into slots 3 of the top and bottom. Because you are installing "Pairs". Take the Stick out of slot 4 of the bottom half, and put it into slot 3 of the top and both should be reconized.

Essentually 1 on top and 1 on bottom go together, 2 on top and bottom go together, and so on. So you need to put both chips into slot 3 if 1 and 2 of each is taken up.
 
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