Something

function addActivity(where) {
  if(isNaN(activities[where])) { activities[where]=0; }
	activities[where]++;
	var activityHTML = '<tr class="activities" style="color: #666666;">
												<td><input type="text" value="HVEM" name="'+where+'_'+activities[where]+'_who" /></td>
												<td><input type="text" value="HVA" name="'+where+'_'+activities[where]+'_what" style="width: 80px;" /></td>
												<td><input type="text" value="20. Oktober 2006" name="'$key.'_1_when" style="width: 100px;" /></td>
												<td>kl <input type="text" value="22.00" name="'+where+'_'+activities[where]+'_time" style="width: 40px;" /></td>
											</tr>';
	alert(activityHTML);
}