La modifique un poco, agregué una nueva opción:
Código HTML:
Ver originalfunction mostrar(frm,num) {
if(num==0) {
frm.usuario.style.visibility='visible';
frm.rfc.style.visibility='hidden';
frm.email.style.visibility='hidden';
}
if(num==1) {
frm.usuario.style.visibility='hidden';
frm.rfc.style.visibility='visible';
frm.email.style.visibility='hidden';
}
if(num==2) {
frm.usuario.style.visibility='hidden';
frm.rfc.style.visibility='hidden';
frm.email.style.visibility='visible';
}
}
<input type="radio" name="rad" checked="checked" onclick="mostrar(this.form,0)" /> <input type="radio" name="rad" onclick="mostrar(this.form,1)" /> <input type="radio" name="rad" onclick="mostrar(this.form,2)" /> <input type="text" name="usuario" /> <input type="text" name="rfc" style="visibility:hidden" /> <input type="text" name="email" style="visibility:hidden" />