Basically. Try to clear off the entire HAZ (Heat Affected Zone), as opposed to just 1/4" where the weld will be. Make no mistake, it WILL kill you. Even outside, place a box fan or something over your shoulder to blow the fumes away. Nasty stuff. Avoid using it if at all possible. If you must use it, you could possibly clear it off with a wire cup wheel on an angle grinder. Perhaps that will leave more actual steel intact... I've never had a problem welding it, but it will cut down on the smoke.
Incidentally, there's another reason you may not want to use galvanized. A lot of paints will not adhere to it, many just flake right off, like Tremclad, Rustoleum, etc. There ARE specialty primers out there for galvanized, you just have to make sure you get one.