"Needed" is a questionable term. From the dozens of trigger jobs I've done I will say that there are some pretty usable / versatile substitutes out there for those who don't have dedicated/professional grade smithing tools.
First, A right sized/small spade tip screwdriver seems to make a good rebound tool. You need one with a taperd tip that will fit into the spring but catch the spring face on it's edge. If you don't have one to fit, just grind a step into an old junker screwdriver.
Second, A good set of knife sharpening stones with 4-5 grades of stone can be used for lots of stuff around the shop including reaching 90% of what you need to do in trigger jobs. I've been using the same Lansky 5 pc set to do everything from hatchets to 1911 sears for 20 years or so now. In a pinch, a couple of sheets of 400, 600 and 1000 grit black oxide sand paper on a hard backing will do a decent job as well. This fine paper (as well as mother mag polish on a cleaning patch/qtip) gets into tight places.
As for the DVD/ instruction, there are ALLOT of you tube video's that will walk you through the process for free.
P.s. One place NOT to skimp is on screwdrivers. Get a decent gunsmith screwdriver set before you bugger up the side plate screws. Been there done that.
hth
