To check if your phone has the update, just plug it into Zune Desktop as usual - it's a small update and installs in seconds (though you do then have to wait a few minutes for the usual backup/restart sequence to finish).
Tethering can be turned on and off using the Settings pane shown. The usual caveats about using your smartphone for 'Internet sharing' apply, of course. Make sure your data plan/tariff is up to the task before hanging laptops and friends' devices to your Windows Phone data connection - we won't be held responsible for any hefty data bill at the end of the month!
Oh, and there will be extra battery drain too - lots of it. So have a charger handy as well!