JS FUNCTION:
	function makeVisible(theObj){
		
		obj = document.getElementById(theObj);
		alert(obj.visibility);
		obj.visibility = true;
		
	}

HTML:

<input type="checkbox" value="1" onclick ="makeVisible('imageUpload')" />	</div>
<div id ="imageUpload" style="visibility:hidden;">
<label>Select an image file:</label>
<input type="file" name="data[Profile][image_name]" size="40" maxlength="255" id="ProfileImageName" /><br />
<input type="button" value ="upload" onclick="uploadReviewimg(document.getElementById('profileForm'),'/profiles/uploadimg','uploadframe'); return false" />
<iframe id="uploadframe" name="uploadframe" src="/profiles/uploadimg"class="noshow"></iframe>
</div>	
<div id="showimg" style="visibility:hidden;">To upload an image, click browse, select your file and then click upload. Your image will appear here when it has uploaded.</div>