Why were women not allowed to be actors during Elizabethan times and what did the "actresses" wear?

Women were not allowed to appear on stage until 1660.  Before this time, acting for women was considered inappropriate and actually illegal.  For one thing, the acting troops traveled around, sleeping in odd places.  The proximity and lack of privacy certainly contributed to the prohibition of women becoming such itinerant actors.

Because of the prohibition of women in theatre, young men-- usually prepubescent--played the female roles and dressed in women's clothing.  In reaction to this condition, there was a condemnation of the Elizabethan theatre by some clergymen who contended that it was sacriligeous for men to dress as men, envisioning it as though it were "cross-dressing," a sexual aberration.

The roles of women who were not young or so very womanly were played by the older male actors.  For instance, this may be why Shakespeare's three witches in "Macbeth" have beards.