If you are still interested in keeping the card, check this out:
You can download the Apple Airport Extreme updater from Apple.
Of course, if this is a rev 2 card, then you might be out of luck since Linksys had changed chipsets from the first to the second revision.
• Apple iMac G5 17" (2 GHz G5) - Mac OS X 10.5.8/Ubuntu 10.04
• Asus Eee PC 901 (1.6 GHz Atom N270) - Fedora 13
• Apple Macintosh Quadra 650 (33 MHz MC68040) - Mac OS 8.1
• "JHVH-1" (2 GHz AMD Athlon XP 2400+) - Slackware 13.1