I'm using a Macro to change the stylesheet in umbraco.  Using Firebug the CSS is getting changed in the head tag, however the UI isn't changing as it does w/test pages.

public string _browserVer = "";
public string _CSSFile = "";

protected void Page_Init(object sender, EventArgs e)

 {            

            HtmlLink css = new HtmlLink();
            _browserVer = Request.UserAgent.ToString();

            if (_browserVer.Contains("MSIE 7.0"))
            {
                _CSSFile = "css/MainIE7.css";
            }

            css.Href = _CSSFile;

            css.Attributes["rel"] = "stylesheet";

            css.Attributes["type"] = "text/css";

            css.Attributes["media"] = "all";

            Page.Header.Controls.Add(css);

}

Is there preferred way to do this or is this the recommended way to do this?