Here's a couple of threads that discuss this issue:
http://forum.shrapnelgames.com/showthrea...se+assault
http://forum.shrapnelgames.com/showthrea...se+assault
http://forum.shrapnelgames.com/showthrea...se+assault
I don't know how easily infantry could KO tanks in WWII.
I do believe it's easier than you think it is.
A single man close to an AFV could be dangerous in WW2. They were trained to attack weak spots on the tank, like the engine cover and view ports.
I know molotov cocktails were very dangerous, I posted a brief animated gif in one of the above posts showing a single Rumanian knocking out a T28 with a molotov cocktail (actual footage).
But I don't know about grenades. I would think a grenade on the weak top armour, engine cover, critical track part, or jammed into a port could do damage. But that may require you to be in the
same hex as the tank.