
And I noticed in the end that the Vulcan that Zephram Cochrane first meets and is sitting with in the bar later has a drink with him. On the table is a bottle and two glasses, one of which Cochrane is drinking, so I think it's safe to assume it's alcohol. The Vulcan takes a drink, looks puzzled, inspects the glass, then the music kicks on and he stands up alarmed, Cochrane sets him at ease, and then he sits back down and takes another drink of the alcohol and looks as if he is intrigued and enjoying the drink.
I am sure that, given that T'Pol acqueisced when dealing with the Andorians, that a Vulcan would succumb and drink alcohol at a diplomatic function and especially to avoid a diplomatic incident. T'Pol's, and Soval's, behavior showed as much. But it didn't appear that Cochrane was insisting the Vulcan try or continue to drink from the glass. It is possible (though unlikely, considering that most-if-not-all beverages that fall under the term "alcohol" in the galaxy rely on ethanol and therefore would have similar taste and smell) that the Vulcans didn't KNOW it was alcohol at first, especially given that there was no doubt a language barrier between them. That's probabaly an interesting story in and of itself -- how Cochrane and the first Vulcans communicated, without UTs or even anyone on the Vulcan ship who spoke English.
I've also always wondered as to the identity of the first Vulcans that landed there and the ship that Cochrane met, there was once a debate about it over at TrekBBS I think, as to whether it could have been Solkar in that group (because he is later cited as the first Vulcan Ambassador to Earth) or if these were just random "surveyers" as Troi mentioned, and were not in fact of a diplomatic capacity.