[María José]

Originally Posted by Rusty

The word especially, always used as an adverb, means:
to an unusual or exceptional degree (This building is especially large.)
to single out one among a range (They were all winners, especially Joe.)
chiefly (There are many great violinists, especially men.)
for a specific or particular purpose (This brush, especially designed for removing pet hair, makes a great gift.)

The adverb specially means:
for a special or particular purpose, person, or occasion
(The program was specially for children.)
(This brush, specially designed to remove pet hair better than any other pet hair remover, makes an exceptional gift.)
(The especially tall building had specially designed turbolifts to carry passengers to the higher floors more quickly.)

As you can see, the last definition of especially and the only definition of specially are quite similar. This is probably why there is a great deal of confusion between the words. As Poli pointed out, however, there are certainly times when they can't (properly) be switched. It's improper to say, "The building was specially tall," for example.

Thanks, Rusty