If a character is drunk, what are the penalties associated to it? Are there any benefits to it? I do remember a special prestige class for monks about it, but I don't remember anything specific in the core rulebook.
Well, the 3.0e Arms & Equipment Guide has a section on drunkenness rules. For each drink, it's a Fort save with a DC per kind of alcohol (10-15). Multiple drinks an hour get a progressive -1/-2/-4 penalty. Failures take 1d2 temporary DEX and WIS damage. If either go to 0 you're out of the action; if both go to 0 you may have alcohol poisoning and have to make another Fort save or start taking 1 point of temp CON damage per 10 minutes.
Cool. I just ran a scenario (Green Ronin's A Dreadful Dawn) that did close to this, there was a moonshine kind of drink that if you finished it you won a jar of gold coins; each drink was a Fort save with cumulative -2 penalty and you took INT damage instead. Three of my PCs just started guzzling it; two ended up unconscious, naked, in bed together, with various things scrawled on their faces and bodies in charcoal.
There are no core rules for the effects of alcohol.
The prestige class you refer to is the drunken master, from Complete Warrior. Its drink like a demon class feature increases Strength or Constitution by +2, while it decreases Intelligence and Wisdom by −2 for each swig the drunken master takes. At 8th level, it gains the spell-like ability for medicinal purposes, which turns allows an already-drunk swig to turn into a potion of cure moderate wounds for him, undoing the usual effects of that swig from drink like a demon, and healing him the appropriate amount. Please note that we have a Q&A on the drunken master’s well-deserved reputation for being a terrible prestige class.
Also note that the rules for the drunken master are particular to that class. Characters without that class are not subject to its rules, so none of the things alcohol does to a drunken master, good or bad, applies to someone who isn’t a drunken master. As described in mxyzplk’s answer, there are separate, general-purpose rules for alcohol in Arms & Equipment Guide, a 3.0e book that you can use in a D&D 3.5e game. On the other hand, Book of Vile Darkness, which is a weirdly “3.25” book published during the development of 3.5e, claims that alcohol should work as a drug/addiction as laid out in its Chapter 3. Those rules only specifically spell out the effects of a particular terran brandy, though, which is explicitly magical (the other drugs laid out in that chapter are equally fantastic, rather than referencing any real-world drugs, though aside from terran brandy they aren’t magical). If you incorporate either of these rules in a game with a drunken master, you’ll have to figure out how drink like a demon combines, or overwrites, those general rules for everyone else.
While far from official, this is my take on the problem:
There's a wine called Jhuild, detailed in the Unapprochable East supplement for the Forgotten Realms campaign setting. This wine is more a poison or a drug than anything else: it gives bonuses to strength and penalties to intelligence and charisma. (It's part of the ubercharger build.) If you fail a save after drinking this wine, you become unconscious. (Now we know what the barbarian drank in the movie The Gamers.) If you pass the save you get -2 to all checks for 12 hours.
I'd rule a common wine is way less powerful than Jhuild. I'd suggest the effect of passing the save with Jhuild could be the effects of failing the save with a regular drink. Unconsciousness could be the result of two failed saves in the same drinking session.
For really strong liquor or large amounts, fortitude saves. Miss those, weakened or sickened conditions. I haven't found any tables in my search; if I do, I will update.