you don't really need a lookup table
let's say you have a table
Code:
tbl_People
PeopleID PeopleFN PeopleLN
1 Mickey Mouse
2 Donald Duck
If you create this query
SELECT * FROM tbl_PEOPLE WHERE ((PeopleFN) = [Enter FN] and (PeopleLN) = [Enter LN])
this will show you the results (this assumes it's possible to have multiple people with the same fn/ln which you have to provide for in any database).
From there you can modify the query if you are lookup up based on the contents of a form etc by exchanging the [ENTER FN] with something like forms!<formname>!<fieldname>.
I just want to caution that any time you look up an ID on your table you have to provide for the possibility that you could have multiple people with the same FN/LN, even if you don't currently have that situation it may happen and if you don't program for it your database will not perform as expected if it does happen.