ill do my best to explain but some of these guys probably have a better answer.
1. You get vac baned once vac detects some sort of cheats runing etc, but its not instant it can take usualy up to a week, Noone usualy pays attention to the little guys who whine to valve/vac/steam.
2.When you get vac baned you cant play any multiplayer games (as far as i know) only singleplayer games (IE. Hl2, Hlf2:ep 1, etc)
3. You dont loose your steam account they just give you a handicap :)
4. As far as i know Vac2 is alive and kicking :), This is known because they have raised the ban levels for vac2 from vac1, vac1 was a 1 year ban, vac2 is a 6 year ban :\
Hope this works for yah :D