Silly questions
1. What OS are you using on the computers? If using XP SP2 do you have the WPA2 client update installed i.e.kb917021?
2.Are the drivers for the wireless cards in your computers WPA2 capable?Normally just download the latest drivers from the OEM's web site.
3.Did you set your encryption for WPA2 Personal in the router and are you using WPA2-PSK
TKIP or AES or a combination? I have problems with TKIP+AES. I also have problems trying to use WPA+WPA2 combination.
4.Does the combination in your computers exactly match that of the router?