Why does my laptop only lock up online?

I have a Gateway 8708:17"/250gig hd/2 gig mem/Duo Centrino running XP Media and using an ATT 881 Air Card and ever since I bought this card my laptop has been locking up..ATT of course says it's the laptop and Gateway says it's the card. I've tried IE7 with Google and does okay. It hates Netscape and Firefox!!! Locks up every few minutes. Has to retype all of this cause it locked up before I could finish. I have flash get,desktop maestro,winrar,avg,spy bot and spy doctor all on my laptop. I've tried the latest of everything what could possibly cause it to lock up only online or connected. Help Me Someone!!!!