Import it to a temp table, then establish a relationship to the contacts table based on the name fields.
This is a quick way to find and see if any temp records show any related records.
If you need to do looser matching (EG match Bob to Robert, mike to michael, etc..), it's possible using the same method, but you need to relate fields based on a list of possible key matches. Creating that list of match keys is much more difficult.
good idea, thanks
I just finished adding something very similar to one of my systems and I used the same Method that Mike recommends. What I then did, is added a search tool that lets me search by just last name (or by other info that you don't have here.) to get a list of possible matches in a portal in a popover so that the user can click to select if that search pulls up a record that should have matched but didn't. (In my case, the lack of a match is most likely due to a marital status change producing a change in last name.)