I am doubt your question is regarding Crystal Report or the form combo box logic?
your combo box should work as cascade combobox.
first fill the item to the company combo box
. then load the city combo when the user select a company. you can load the city combo with cbCompany SelectedIndexChanged event.
you have to modify the City combo stored procedure as
string selectedCompany= cbCompany.SelectedValue;
cm = New SqlCommand("Select distinct City From Staff Where Company='" + selectedCompany + "'", cn)
I'm not much familer with VB.net coding. may be syntax are not correct.