[H] Thinkpad wireless problems

[Winterlight]

I am trying to troubleshoot a Thinkpad R51 ...circa 2004. It is 
running XP PRO SP2, and it is fully patched. The problem is that it 
will not connect to any encrypted wireless network. It has no problem 
connecting wirelessly to a unprotected network, but it refuses to 
connect to a protected network.... any protected network, even one it 
previously had no trouble connecting to.

At first I thought it had something to do with the IBM wireless 
adaptor, so I updated it to the latest posted drivers. That didn't 
help but it did cause all the old wireless addresses to disappear 
from XP wireless network setup. There was one local protected address 
that was working on that list.... but now it won't even connect to 
that protected network.

I'm stumped...any thoughts.