The 50 series units do not have physical wifi on/off master switches, only the 60 series onwards. operation is controlled purely by FN+F5, which requires that you have the HOTKEY software installed -
http://www-307.ibm.com/pc/support/site.wss/document.do?lndocid=MIGR-68000.
If
you have the correct drivers, and there is a choice of 4 different types of wi-fi card installed on all R51's, you need to visit the Lenovo site and input your model (2888) and type (???) to get an exact match to your system. Here is the rough list
http://www-307.ibm.com/pc/support/site.wss/MIGR-55029.html#wireless
If you also have Access Connections installed (in the ThinkVantage group), this controls all wifi connections, so using the XP built-in wifi support as your screen-shot says, Windows Cannot Control this Connection, as its not being controlled by XP. To use XP you must remove the Access Connections software.
Using the System Update software, should allow you to automatically connect to Lenovo and update ALL your Lenovo related software and drivers - it scans for what you have, and compares that to the latest versions on the site.
in short, you need to know the model of wifi card, get the right drivers from the site, make sure you have the HOTKEY software installed, remove Access Connections if you wish to simplify the wifi usage in XP and check for any other software updates.