The D-link DWL 122 seems to very buggy drivers on OS X: when you unplug it while your Mac is on, it often crashes with a kernel panic. How can you avoid that?
Go to your System Preferences, then Network, then click Show and choose Network Port Configurations from the pop-up menu. There you can find "Ethernet adapter (en1)." That is your wifi dongle; uncheck the "On" checkbox, then click "Apply Now." Now you can unplug your dongle without any fear :)
Remember to tick it back to On if you want to use your dongle again. This hint is useful for other wifi dongles using the same chipset and drivers (e.g.: NetGear ma111).
Mac OS X Hints
http://hints.macworld.com/article.php?story=2006030110481954