A lot of women are concerned about beginning a strength training program because they don't want to end up with large, bulky, body-builder muscles.  But because of genetics, hormones and women's natural body types, this is highly unlikely.

The average woman doesn't have near the testosterone of the average man and therefore can not build any where near as much of a large muscle mass as a man can.

Most often, strength training helps women tone up muscles they already have.  A woman can experience a 20% to 40% increase in strength after a few months of consistent strength training. 

As their strength grows, some women will experience a small increase in muscle mass.  If this is a concern, and it really shouldn't be, seek out a certified female personal trainer who can help you avoid or minimize this effect.