Don't install the latest Windows update KB886185 if you have a wireless network. I installed it on my laptop and it was unable to access the network. Uninstalled it and it was OK again. Repeated the install - no network access. Uninstalled it again - OK. Hopefully some of you will read this and save yourselves an hour of wasted time.
Did you restart the computer? Or also if you have firewall on, try turning it off and on. My network is fine since this update. Also, you could try removing the network from a trusted zone, then set the network upagain.
A restart was required after the update. The XP built-in firewall was enabled on the laptop, but I tried turning it off and it didn't make a difference, though I guess I'd be more secure with the firewall but without the patch than the other way round.
I never have trouble with this wireless network so it just seemed too big a coincidence that this happened after installing the update. I was going to be good after SP2 and do all the automatic updates, but after this I think I'll go back to disabling updates and relying on my SMC firewall to keep out the bad guys. It just wastes too much time when an update screws up the system.