Wifi adapter loads CPU

I do not know whether I should put this question in the CPU forum or in wireless networking, as it kinda combines the two. Anyway, I have a wireless D-Link DWL-G550 adapter. When I connect to my wireless network, the CPU load goes to 100%, which of course, slows down the computer tremendously. On a few occasions it did not happen, and connection to the network did not cause this problem. But as a general rule, it does. I can't figure out what causes this problem. It seems quite unique as Google did not return any results on my query about this problem.

Sorry, I should have provided this info before.

OS: Windows XP Professional SP2

I have tried two versions of the driver that I could find on the Internet (v. 1.20 and v. 1.40) the same result.

Most surprising thing: the task manager shows between 5-30% load between two or three processes (I sorted processed by CPU load to single out those which load the CPU), while the graphic representation of the CPU load shows 100% load, and the task manager states that CPU is loaded 100%