Wireless connection drops/no connectivity

Hi,

I started some consulting work for a company that uses a wireless connection with 2 access points in their office (one on channel 6, the other on channel 11). They use a WPA-PSK key to secure the connection.

The problem is that with about 70% of the laptops that come preimaged from the parent company the following problem happens.
You try to connect to the wireless, enter the password, the authentication passes, an IP address is assigned, it appears connected, about 5 seconds later the connection is dropped, the computer tries to reconnect, it reconnects, then it drops and stops connecting.

I have tried the following things:

• Disable all firewalls/antivirus
• Reset the TCP/IP stack (using netsh int ip reset c:\resetlog.txt
• Reinstalled the drivers of the card
• Tried different software besides the Windows Wireless Zero Configuration (like the software for that driver)
• Winsock repair

The other two things I tried with some success is:

• Connecting to another wireless connection - worked but only for unsecure
• Reformatted Computer (or Repaired Windows installation) - worked for 4 of the 5 computers I tried.

Now the other 30% have a similar yet annoying issue. Everytime I connect to the wireless network I get a limited, no connectivity message. I tried the same kind of things I did above but nothing worked. I'm not sure what the problem is, with one computer i actually replaced the wireless card (only to get the issue that i was getting at the top). Reformatting worked once out of 3 times on this issue.

If anyone has any ideas please let me know (especially if there is a way to fix this with out reformatting).

Here are the kinds of computers that i've been working with if its important:
Lenovo R61e
Lenovo R61i
Lenovo 3000 C200

• The lenovos all have either one of these cards:

Intel Pro/Wireless 3945ABG
Intel Pro/Wireless 2200bg

Dell Latitude D620 - Dell Wireless 1390 WLAN Minicard

EDIT: These computers are all post SP2 (installed windows xp with sp2 included) so it does include the WPA patch.