The Very End - it's all about slip angles, you need to slip the tyres to get the most grip - on most cars the slip angle is very VERY small, ie unnoticable, however on old F1 cars with old tryes (ie the 60's) the slip angles were larger and so 4-wheel drifts were more aparent. On a loose surface a large slip angle helps too.
Drifting is about getting the biggest angle, going closest to the (whatever), holding it the longest and speed. Not about going round a bend faster...
EDIT - *sigh* I'm arguing because someone earlier used the "drifting is racing" line...