I got the achievement legitimately on the PC. It was difficult, but with a good team and some luck you should be able to do it. Now Left 4 Dead 2, I haven't even tried. I find that game much harder with my play style, probably because I relied heavily on shotguns, melee attacks and pistols in the first and now those things are not as easy to abuse. Plus my regular play group kind of broke up.
One achievement I never went to the effort to do was Nothing Special. We tried maybe a handful of times, but it is not fun at all to do, since about a half hour of work can be made worthless in a few seconds.
As for defeating the tank with melee weapons only, it's very doable, but you need 4 people together who are achievement hunting and some coordination. The tank takes a while to turn corners and turn around (although at one point there was a bug where he would lumber toward you backwards and be facing you as the computer believed) and also to climb objects. If you can kite the tank into climbing a ledge you have a good block of time to wail on him. Then you need the person who has aggro (dealt most damage most recently) to run away, loop around a building or something to get some distance on him and trick the tank into climbing again.