1 field - "Lastname, Firstname"
This I would not do. One field for first, one for last. The first suggestion given by RG is the best option IMHO. Names aren't a great identifier anyway. You really can't make either field unique as you should allow for 2 John's. Nor can you make Smith unique; nor can you make a unique index on them, since you should allow for 2 John Smiths. If you have unique employee id's, I suggest you have that in the first table and in the second, have that long data type field which is the autonumber for the employee which comes from the first.
Suggest you read up on some of these sources if you're really new to Access. They may save you headaches later.
http://access.mvps.org/access/lookupfields.htm.
http://access.mvps.org/access/general/gen0025.htm
http://allenbrowne.com/AppIssueBadWord.html
https://access-programmers.co.uk/for...d.php?t=225837
http://www.utteraccess.com/wiki/index.php/Autonumbers
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.