You could do several things.
Create a new table, which you may wish to call Personel or something along those lines. Add all the possible names to this table.
Then on your form create a combo box for Act 1. Follow the steps in the wizard to link the combo box to the Personel table and store the data in the appropriate field of whatever table your form is based off of.
This is the best way to create a data lookup field. However, you can skip building the table if you wish, as the combo box wizard should provide you with the option of entering values to appear in the combo box. This second method may be a little difficult to add or subtract names as your personel may change over time though.
What sort of duplicates are you wishing to avoid? If the same personel is in Act 1 and 2 then the fields would naturally contain the same data. Let us know if we can provide any more assistance.