i want a drop down list in the Zip Code field in the Secondary tbl so that once i pick a value from this Zip Code drop down list (these will be the Zip Code values in the base tbl), the corresponding values of the State and Country from the base tbl will appear at the same time in the secondary tbl.

Can't be done in a table.

You have to use a form and also add some code to the afterupdate event procedure of the combobox used to select the zip code.
It woud be something like..(assuming zipcode is the first column in the combo box)

me.txtState = me.comboname.column(1)
me.txtCountry = me.combobane.column(2)