And you're sure that this isn't the Airport Extreme card? Because I don't think the AE card will work on the Cube.
Also, have you upgraded to the latest version of Tiger? 10.4.4 was just recently released, but you might want to wait on that one if you're not quite sure. 10.4.3 Combo Updater should still be available from Apple's website. Just make sure you're downloading the Combo Updater and not the "Delta" Updater which only upgrades from 10.4.2 to 10.4.3.
• 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