No mention of part number for the AirPort Card upgrade, so you're undoubtedly right about it being the original. Thankfully, installing it should be a piece of cake, it's behind the CD bezel and all you need in the way of tools is a #2 Phillips screwdriver.

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Thanks to Wikipedia, I found out my model is the ATI Graphics model. Thanks to Apple.com, I found out the AirPort Extreme card works with eMac (ATI Graphics) and newer. And to you and ifixit, just open the disk drive, unscrew the 2 screws see able, put in the card and put the screws back in.

Sadly, its not the USB 2 model. Boo. Still can't beat $10! Also came with original keyboard and a off brand mouse.