I had started reading Lure of the Nile months ago, but haven't been able to get further in it for a while. I've read most of the portion Saladin was Keeper for, except for the last two pages, as well as the background material. I've also been reading the Dark Ages campaign The Winter's Howl, the Gaslight campaign The Season of Our Discontent, Carcosa Rising, and Laraqua's The Last Express. I read Hurricane Cthulhu, which is over, but jabonko mentioned that there would be a sequel. I've read the beginning of a few other campaigns there, but they move too fast and I just don't have time to follow all of them.
The chainsaws are more something for later - there are two of them in the truck - though they could be used to cut the lumber. They do 2d8+db damage. An average head hit on a zombie from someone with a positive damage bonus will be enough to kill one.
If you were asking how much damage the M249 SAW does, that's 2d8 per bullet, as it's a 5.56mm weapon. Delta Green rules list it as 2d6, but the basic rules say 2d8 and we've been playing with the higher damage so far, so we'll continue to use that.
The SAW can fire bursts with a maximum rate of 20, and it can be fed with a belt of 100 rounds or loaded with a 30 round magazine. You would only roll once to hit for the burst. If the burst hits, you will roll 1dX to see how many bullets hit, where X is the number in the burst (up to 20). You can also spread a burst between multiple targets if the angle between them is small, and in that case you make one roll per target, but the total number of bullets sent towards all targets can't exceed 20. It's also quite possible for stray bullets from a burst to hit other things in the line of fire, so be careful!