var counter = 5;
var limit = 100;
function addInput(divName){
    if (counter == limit)  {
        alert("You have reached the limit of adding " + counter + " inputs");
    }
    else {
        var newdiv = document.createElement('div');
        newdiv.innerHTML = '<table class="searchbox"><tr><td class="searchlbl" style="padding-right:10px; width:90px; text-align:right;">' + (counter + 1) + '.</td><td class="searchfld" style="width:220;"><input class="formfield" type="text" name="firstname' + (counter + 1) + '" style="width: 200px; color: black;" value="" maxlength="100" /></td><td class="searchfld"><input class="formfield" type="text" name="lastname"' + (counter + 1) + '" style="width: 200px; color: black;" value="" maxlength="100" /></td></tr></table>';
        document.getElementById(divName).appendChild(newdiv);
        counter++;
     }
}