I have also resolved this problem and for your information here is the solution:

        protected void lstContent_ItemDataBound(object sender, System.Web.UI.WebControls.DataListItemEventArgs e)
        {
            ((HyperLink)e.Item.FindControl("theLink")).NavigateUrl = formatLink(((RandomLink)e.Item.DataItem).LinkAddress);
        }

        private string formatLink(string Url)
        {
            int testNumber = 0;
            bool IsPage;
            string retUrl = "";
            try
            {
                testNumber = Int32.Parse(Url);
                IsPage = true;
            }
            catch
            {
                IsPage = false;
            }

            if (IsPage)
            {
                retUrl = PortalSettings.HomeDirectory.Replace("Portals/" + PortalId + "/", "tabid/" + testNumber + "/") + "Default.aspx";
            }
            else
            {
                retUrl = Url;
            }

            return retUrl;
        }