I can't find the vid online, but Will Ferrell played the cowbell with Queens of the Stone Age when he hosted a couple seasons ago. So maybe you were thinking of both performances and got them mixed up? Either way, the QOTSA performance was hilarious. I'd look for that too.
Librarians and homeless shelters around the country are making emergency preparations for dealing with the hordes of newly-liberated teens who will have nothing else to do except read and do community service now that TRL is gone.