I quit smoking about 8 months after I quit drinking. I've quit smoking so many times I can't count. The longest time was maybe 6 months and I'd usually start smoking again after a trip to a bar with a smoker friend. Alcohol, one way or another, would get me to start smoking again, and usually when I least expected it.
That was about 18 months ago. While giving up nicotine certainly seems to get harder the older I get (and one of the biggest deterrents I have now too), not having the alcohol around makes not starting alot easier.
You know yourself the best. If you can give both up at the same time, go for it. But take it easy if you think giving up both at the same time might cause you to take both back up again.