no you don't need to grind off the galvanization. I worked for a welder who did chain link fencing. He used galvanized steel pipes all the time. Not once did he clean them off, also when you weld the stuff be careful. I know that working a weekend around the crap can make you very sick for the weekdays.
When Hk gets here he will give more advice.
As for doing it yourself, clamp it in place with a very small gap if you can. That way the weld will fill the tiny gap becoming smooth.
Also a note for doing it yourself. Keep it cool. Otherwise the metal may warp and you will need to fill it alot more than if you don't warp it. To do this just tack weld it in place, then do small welds about an inch apart. Go around the entire patch, leaving these gaps, then if the area where you started is cool, do it over again. You may possibly wanna go around two or three times to keep the metal cool. At least this is how me and my buddy did it on my car, and it turned out pretty good.
