sounds a bit like my topic in:http://forum.thinkpads.com/viewtopic.php?f=2&t=71664&sid=a2b23361077314fb3e287a2d59afb0cd
I have so far solved it by using Intels software instead of WinXP's or Lenovos Access Connections.
Here is the link to Intels SW:http://downloadcenter.intel.com/filter_results.aspx?strTypes=all&ProductID=944&OSFullName=Windows*+XP+Home+Edition&lang=eng&strOSs=45&submit=Go!
It's item 4 on the list!
As I mentioned in the other thread, I found that in Linux (Ubuntu 8.10 in my case) there was no problems. And it is very strange, that in some places, Windows would connect to a much weaker network found, and not being able to find one a few yards away - sometimes after a few attempts, but definitely not a stable solution. So far I'm pretty happy about the Intel Software