I'm experiencing the same problem...at least once a day.
I've found the solution to my problem in a different thread based on a different model of wireless card. For an odd reason, having 802.11n mode activated was short-circuiting my card and causing it to shut off every 2-3 minutes. Try disabling that mode and see if it fixes your problem. Otherwise, I can only suggest making sure your drivers are up to date, that the problem isn't associated with your modem/router or that maybe you should try reinstalling the card.
Hope that helps.
Same problem on a precision 6600 laptop.
Haven't resolved it yet. I installed the most recent drivers from the intel site and am still having the same problem. Nothing that requires a persistent network connection will work properly, though I can browse the web intermittently. It seems to happen every few minutes.
Intel suggested settings to disable Power State Polling aren't available in the newest drivers, at least not for me.
I'm about to call dell and demand they send a new card.
Have you tried turning off 802.11n mode? Your problem sounds very similar to mine and that's what solved my frequent time outs. Let me know if that doesn't work.
The thing is, I kinda want N mode to work. I bought the card for its bandwidth.