Airport Card
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Apple has discontinued the Apple Card for the Apple Extreme card. However not all computers can use the new card.You can search ebay for Apple Cards, but they cost $129+. Which is a lot of money to spend to make your desktop computer wireless.
I found a cheaper solution this weekend. I bought a DLINK USB Adapter (DWL-G122) for $45. I downloaded some third party driver and was able to connect with no problems. (Search for Macintosh USB Wireless for the Driver.)
This is a short term solution, over the next few months, I'll be building a home network that will replace the wireless connection.