Here are some things you can try with increasing severity...

1) Go into network connections, find your wireless network connection icon, right-click it and disable it. Re-enable it and see if you can get online.

2) as above, but reboot after disabling, and once your computer comes back on, re-enable.

3) Go into Device Manager, find your wireless network adapter, uninstall it, and reboot the computer. Vista should detect it and hopefully automatically install it again. You may need the driver disk that came with your computer though.

Honestly there's only a 50/50 shot this addresses your problem, but its worth a try, and you'd kick yourself if you didn't do it before you threw your compy out a window