Legally, as in if you were breathalysed you would be ok but even one drink can distort your ability to drive....and as one drink usually leads to another it's best to abstain altogether.
I metabolize alcohol differently on different occasions. Sometimes one drink can give me a significant head buzz. It depends on how much and what I've eaten for the last few days, how hydrated I am, and what the weather is! So.....it could be the case for you as well.
I don't understand how it happens, but a cold beer in the hot summer sun can send me up dancing on top of picnic tables. : )
Most people can only “burn off” an average of about 0.016 grams percent of ethanol (drinking alcohol) per hour.
Some hints: (1) Eat first, especially high protein foods; (2) Don’t drink alcoholic beverages that have carbonation mixed with them; (3) slow down the alcohol intake so that your body has adequate time to process the alcohol (110 pound female, one standard drink per hour); (4) wait at least 2 hours after the last drink to start driving, SO LONG AS you feel no “buzz” at all.
With only one drink, if you will follow those suggestions, you should have no problems.
It takes an hour to an hour and a half for your body to fully metabolize an ounce and a half of alcohol, so however much you drink, the safest option is to not to drive until 2-3 hours after your last one. Which probably means that a drink or two at the beginning of the party is fine, as long as you stop. Safest to abstain, as rudyboo mentioned, it's tough to stop when the party's in full swing and you already have a buzz.