you _could_ do that, but it's not a good way to set up a relational database, it is not proper data normalization. It leads to having to much unneeded repeating data amongst other issues (what happens if the first name and last name in the other table gets updated?)
Instead, you should store the ID for the user.
on the page where you will be showing the data from the table, use a joined query to return the related data from both tables.
see the following page for more details on joined queries: