if (document.all["inputName"].style.display == "none")
document.all["inputName"].style.display = "";
else
document.all["inputName"].style.display = "none";
document.all["inputName"].style.display = "";
else
document.all["inputName"].style.display = "none";
....
<input type="text" id="textbox">
<input type="button" onclick="javascript:form1.textbox.style.display=='none'?form1.textbox.style.display = 'block':form1.textbox.style.display='none';">
...
</form>