There's no Airport update.
Download & install this wireless monitor utility MacStumbler http://www.macupdate.com/app/mac/8035/macstumbler
It should pick up your wireless router & you can watch the signal levels.
The problem is not that it won't connect to Wifi but that it is unreliable.
It can connect and work fine for anything between 2 minutes and 1 hour. Sometimes it will completely disconnect and refuse to re-connect for a couple of minutes. Sometimes it will give me full bars and i can use youtube and all without problems.
I have opened it up (WOW massive hassle) and checked the airport card. The antenna was plugged in properly.
Do you have other wireless devices connected to this wireless router?
If you do, then do those devices have the same issues?
I suspect the problem could be related to the channel your wireless router is set on. Try changing the channel to something like 7 or 8. See if that provides you with a solution.
This has happened to me in the past, where the computer would work fine for an hour and then suddenly drop connection. On changing the wireless channel improved my signal.
Best of luck