One Windows XP computer at home took a 10 to 15 minutes to connect to our wireless network. Its Wireless Network Connection Status dialog would show a status of Acquiring Network Connection and that the computer was receiving packets from the wireless router but no packets were being sent from the computer. There was no problem connecting to the router using a wired connection.
Our other computer connected with no problems, the wireless router's configuration had been re-done to avoid clashing with the neighbours' networks and the computer's DHCP service and its dependencies were running. I started Windows Task Manager when the computer started and watched which processes were launched. When the wireless connection was finally established, I saw that ZCfgSvc.exe was also launched. Checking the list of services, the Wireless Zero Configuration services was disabled. I configured it to start automatically, re-started the computer and now the computer establishes a wireless connection within a couple of minutes. Microsoft has some information on solving this problem.
(Lest it sound like I knew what I was doing, I've been working on this problem off and on for a month. I had reconfigured the wireless router and computer's wireless adapter numerous times and searched high and low on the Web for an answer.)
11 Feb 2007. Ergh, wrote too soon. Another computer that was connecting successfully started having the same problem. This is too weird. Time to try a different tack.
This time, I reconfigured the router and network adaptors to use 802.11b/g instead of just 802.11g. The second computer started connecting again.
Back on the first computer, I used the Intel PROSet software to manage the network adaptor. That computer stopped connecting again. When I let Windows manage the network adaptor again, all was fine.
So it seems that different solutions are required at the moment for the two computers. One possibility is that the first computer was newer and had all Windows updates installed, while the second computer never had an update installed.
One hour later. I installed all 69 (!) Windows XP updates on the second computer and sure enough, it couldn't connect to the wireless router if I used the Intel PROSet software to manage the network adaptor. Switch to the Windows client and reboot. No problems. Turn on both computers and connect. No problem. Think I've finally solved it.