try this instead:
javascript in head section of html
<script type="text/javascript" language="Javascript">
<!--
function hideMe(){
// Hide or show iframe
if(document.getElementById("myframe").style.visibility = "visible"){
document.getElementById("myframe").style.visibility = "hidden";
}
else{
document.getElementById("myframe").style.visibility =" visible";
}
}
//-->
</script>
body
<input name="shrani" type="submit" id="shrani" value="Shrani" onclick="hideMe()" />
<iframe id="myframe" width="100%" src="vnosPozicija.php" style="visibility:hidden;">Alternate I-frame content here!</iframe>
---
I just made a few changes to yours (extra "=", missing ";", missing "}")... I used code similar to that to hide elements in a div tag.
Hope that helps!