PLEASE HELP ME about choosing entries while entering data to fields

Can anyone help me about how can i configure it to be able to choose
only some types of data (for example to enter the name of the city to
one of the columns [or fields] the one who is entering th data must be
able to choose only the cities that i want to be added and how can i
make it possible to seem like a drop down menu in pgAdmin II or in
pgAccess  it while someone entering data to the postgresql) while
entering new data to postgresql in pgadmin II or in pgaccess .....
Thank you .....

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  Research Assistant
  Himmet KARAMAN
  Istanbul Technical University
  Geodesy and Photogrammetry Eng. Department
  34469 Maslak/ISTANBUL TURKEY
  Tel    : +90 (212) 285 67 83
  Fax    : +90 (212) 285 34 20
  Web    : http://atlas.cc.itu.edu.tr/~karamanhi
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