i want a field to become visible or pop-up only when a certain checkbox is marked...
now how do i get that done?

If Me.Checkbox = -1 then
Me.OtherField.Visible = True
Else
Me.OtherField.Visible = False

You can put this code in the On Current event of your form or the After Update event of the checkbox, depending on when you want to trigger the code....