RE: Look-ups
Make sure your list is set up nicely.
VLookup can't look left, so if you have a list containing first name, last name, telephone number and userID in that order and you will be doing a VLookup to return the last name based on the userID, you'll have to have the userID more to the left than the last name, if you get my drift..
So your list should be userID, first name, last name, telephone number now.
Otherwise you will be looking at using the index() and match() formulae together as array entered formulae (don't ask!), which is difficult to enter these formulae and clogs up your system a fair bit too.
Hope this helps
Paul