Remember the ThinkPad T42 I bought last year? It's still running XP and doing fine, thank you.
I run 802.11g throughout the house and the T42 came with a 802.11b mini-PCI card. I found a P/N 91p7301 on eBay for less than $5. Swapping it out wasn't trivial but I did it and it works fine.
I had installed Windows XP SP3 on a number of systems and had had NO problems.
After I finished the SP3 install and rebooted, the network wouldn't connect. It just sat there saying it was trying to get an IP address. Of course I tried "Repair" but no change.
Interestingly, if I left the wireless NIC trying to connect and connected the wired NIC to the router, the wireless NIC got an IP address and all was well.
I got another laptop and began Googling it. I found a couple of hits here and here. I wasn't alone.
It seems to be pretty specific to the particular chip set that's in that Wi-Fi card. The suggestions were to set the services "Extensible Authentication Protocol Service" and "Network Access Protection Agent" to "Automatic" and reboot.
Oh, I don't use ThinkPad's "Access Connection" nor nLite.