XP Laptop will connect to WPA but not WPA2 wireless network

I have 3 XP laptops that will connect to WPA but not WPA2 wireless network. What do I need to do so that these laptops will connect to the WPA2 wireless network.

1 of the WPA2 networks requires a cert from my company which I have installed, but says it can’t find the correct cert.

The other WPA2 network just requires a password, I enter the password, and verified the password is correct, but it will never connect.

Any suggestions.