the think pad thing is only if your using a secured network
Skip the issue we've seen is trying to be able to select the SSID. If the Windows Wireless tab isn't in control you still have to make is select in the Thinkpad software. I love Thinkpads, but we abandoned their "IBM Access Connections" just because of these issues.
Dave on another note, I was writing something else in here and it reminded me of another issue we battled between a Linksys WAP and a Thinkpad. Is the Thinkpad an earlier generation like a T30? If it's 802.11b just for testing purposes go into the WAP and set it for "B ONLY"
and see if that fixes the problem. I'd forgotten about battling that about 2 years ago when it was set to auto select.
Edit: Dave what Model Thinkpad is this? I've got a lot of those laying around here and I'd like to play with some of the settings. Also go into IBM Access Connections and make sure you don't have any profiles enabled. Lastly, and I'm sure you've already confirmed this, but in the Network Connections Properties, on the Wirless Networks Tab, double check to make sure IBM didn't uncheck the box at the top that says, "Use Windows to Configure My Wireless Network Settings."