[Javascript] Change a form object

[Reuben D Budiardja]

Hello,
Is there any way I can change a form object in javascript? What I mean, 
if I have a

<INPUT TYPE="TEXTBOX">

can I change it to 

<SELECT NAME="select_something"><OPTION NAME="bla"><OPTION 
NAME="bla2"></SELECT>

by using javascript, say if a user click/unclick a checkbox?

Thanks for any suggestion.
Reuben D. Budiardja