Tis very possible my friend....

lets say your 3 input fields are name1, name2, and name3
and your dynamic text field is nameFinal

you have a submit button, the actions on this button should be....

on (release) {
nameFinal+=name1;
nameFinal+=" ";
nameFinal+=name2;
nameFinal+=" ";
nameFinal+=name3;
nameFinal+=" ";
}