how to take the text as input with out using grammar

Hi
    I don't know how to take the text as input with out using the grammar. if i tries to read it in the fallowing format

<field name="username">
      <prompt bargein="true">Please Spell the User name</prompt>    </field>
 
It should not accepting for any input. My requirement is i want to give one text(string)  input. And that text is a dynamic text. 

so please give the solution to my problem as early as possible.

Thank you

regards
ganesh