boingk,
hangover is caused by acetaldehyde toxicity by saturating alcohol dehydrogenase enzymes with ethanol. methanol poisoning is near impossible due to the relative concentration of methanol in ethanolic beverages considering they are competative substrates for ADH enzymes. In short, you'd die of ethanol poisoning way before you'd even feel ill from any methanol poisoning.
In fact, it wasn't too long ago that the emergency treatment in hospitals for methanol and antifreeze poisoning (ethylene glycol, another ADH substrate) was actually to give them ethanol, so their ADH chewed on ethanol instead of the more toxic substitutents.
i do agree though, water helps, and dehydration can make you feel pretty crappy. but again most beer is like 95% water and ethanol doesnt dehydrate you *that much* to negate the water that you're consuming at the same time.