ActionScript 3.0 :: Loading A Symbol From The Library (with A String)?

I am trying to load a movieclip from the library onto my stage. But the name of the movieclip is read in from a user-entered text field. Typically, to load a movieclip from the library named, Bee, I would do the following:

var mc:MovieClip = new Bee; // this works.

But the name of my symbol is in a TextField. The following do not work:

// Attempt #1:
var mc:MovieClip = new userfield_txt.text; // No Good
// Attempt #2:
var str:String = userfield_txt.text;

[code]....

I realize the new operator requires a Class data-type, so how do I get the value stored in a String or TextField into a Class type?