i need a driver dbexpress for connected to postgresql with delphi 7

i  need a driver dbexpress for connected to postgresql with delphi 7
 
i tried the driver  pgexpress of vita boom , but it is a trial demo.
  
i liked design my own driver dbexpress , where i can get the
 information for this . ?
  
I don't  want use the ODBC driver , but it its very weigth for the
 client side .
  
thanks.
  
Mario Jose Canto Barea