Airport Card
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.