Mine

package com.socialfeedr.behaviors;

import wicket.ResourceReference;
import wicket.Session;
import wicket.behavior.AbstractBehavior;
import wicket.markup.html.IHeaderResponse;
import wicket.protocol.http.ClientProperties;
import wicket.protocol.http.request.WebClientInfo;

public class IEPngFix extends AbstractBehavior {
	private static final long serialVersionUID = 1L;
	private static final ResourceReference PNGFIX_JS = 
		new ResourceReference("pngfix.js");

	public IEPngFix() {
	}
	
	public void renderHead(IHeaderResponse response) {
		WebClientInfo client = (WebClientInfo)Session.get().getClientInfo();
		ClientProperties properties = client.getProperties();
		
		if(properties.isProprietaryIEPngAlphaFilterRequired())
			response.renderJavascriptReference(PNGFIX_JS);
	}
}