Here's something that has me confused.
In the Half-blood Prince, an elaborate plan was made to sneak the Death-eaters into Hogwarts to kill Dumbledore. Draco took his time to devise the plan by using the Vanishing cabinet in the RoR. In the movies, there isn't much explanation but the book mentions that Draco found out about the vanishing cabinet from a boy who was stuck between the pair of vanishing cabinets and how he managed to apparate out of it.
According to HP wikia (here: http://harrypotter.wikia.com/wiki/Vanishing_Cabinet):
Fred and George Weasley shoved Graham Montague headfirst into the broken cabinet on the first floor of Hogwarts when he tried to take points away from them. Montague eventually escaped (by Apparating) and was found in a toilet's u-bend by Draco Malfoy, who summoned Professor Snape for help. Montague revealed the previously unknown powers of the Cabinets to Draco.
How could someone apparate within the school when there were a bunch of enchantments to avoid the very same thing. Because when Dumbledore apparated with Harry to retrieve the horcruxes, he clearly mentions that he lifted the enchantments temporarily.
And if there weren't, why couldn't the Death-eaters (or anyone else) apparate their way into the school?