WiFi connection brings CPU to 100%

After about a year of not using one computer, I decided to give it to my son. So, I re-installed the system (Windows XP SP2). During the re-install the system locked up.. after a few minutes I touched the computer case, and it was hot. It turned out that the PSU fan was not working. I made it work, and as a result I managed to re-install the system (all over again) and have an operational computer. I have no complaints about it, except for one thing. It has a wireless D-Link DWL-G550 adapter, and when I connect to my router and establish Wi-Fi connection, the CPU load goes to 100% and stays this way until I disconnect. When I look at the processes in the task manager, none of the processes take up 100%.. I might have between 5-30% load in the processes window, but when I go to the graphic representation of the CPU load it is at 100% all through the time of my Wi-Fi connection. Once I disconnect it drops to usual 1-5% in idle state...A year ago, when I used this computer, I had no problems with having Wi-Fi (though the set up then was different, I used Wi - Fi as Ad Hoc connection between the two computers).

This is the story. If anyone has any ideas about how I might get rid of this CPU load during Wi-Fi connection, I'll be more than happy to try them. Thank you.